IITJEE2010-Paper 1-CMP-1

FIITJEE Solutions to
IIT-JEE-2010
PAPER 1
CODE
3
Time: 3 Hours
Please read the instructions carefully. You are allotted 5 minutes specifically for this purpose.
INSTRUCTIONS
A. General:
1. This Question Paper contains 32 pages having 84 questions.
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11. Darken the appropriate bubbles below your registration number with HB Pencil.
C. Question paper format and Marking scheme:
12. The question paper consists of 3 parts (Chemistry, Mathematics and Physics). Each part consists of
four Sections.
13. For each question in Section I, you will be awarded 3 marks if you darken only the bubble
corresponding to the correct answer and zero mark if no bubbles are darkened. In all other cases, minus
one (−1) mark will be awarded.
14. For each question in Section II, you will be awarded 3 marks if you darken only the bubble
corresponding to the correct answer and zero mark if no bubbles are darkened. Partial marks will be
awarded for partially correct answers. No negative marks will be awarded in this Section.
15. For each question in Section III, you will be awarded 3 marks if you darken only the bubble
corresponding to the correct answer and zero mark if no bubbles are darkened. In all other cases,
minus one (−1) mark will be awarded.
16. For each question in Section IV, you will be awarded 3 marks if you darken the bubble corresponding
to the correct answer and zero mark if no bubble is darkened. No negative marks will be awarded for in
this Section

Write your name, registration number and sign in the space provided on the back page of this booklet.

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IITJEE2010-Paper 1-CMP-2

Useful Data
Atomic Numbers: Be 4; C 6; N 7; O 8; Al 13; Si 14; Cr24; Fe 26; Zn 30; Br 35.
1 amu = 1.66 × 10−27 kg R = 0.082 L-atm K−1 mol−1
h = 6.626 × 10–34 J s NA = 6.022 × 1023
−31
me = 9.1 × 10 kg e = 1.6 × 10−19 C
−1
c = 8
3.0 × 10 m s F = 96500 C mol−1
RH = 2.18 × 10–18 J 4π∈0 = 1.11× 10−10 J−1 C2 m−1

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IITJEE2010-Paper 1-CMP-3

IITJEE 2010 PAPER-1 [Code – 3]

SECTION – I (Single Correct Choice Type)

This Section contains 8 multiple choice questions. Each question has four choices A), B), C) and D) out of which
ONLY ONE is correct.

1. The synthesis of 3 – octyne is achieved by adding a bromoalkane into a mixture of sodium amide and an
alkyne. The bromoalkane and alkyne respectively are
A) BrCH2CH2CH2CH2CH3 and CH3CH2C ≡ CH B) BrCH2CH2CH3 and CH3CH2CH2C ≡ CH
C) BrCH2CH2CH2CH2CH3 and CH3C ≡ CH D) BrCH2CH2CH2CH3 and CH3CH2C ≡ CH

Sol. (D)
CH3 − CH 2 − C ≡ CH 
NaNH 2
→ CH3 − CH 2 − C ≡ C− Na +
3 2 2 2 2 3 3 2 2 2 2 3

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IITJEE2010-Paper 1-CMP-4

Sol. (D)

O CH3 
HBr
→ OH + CH 3 Br

4. Plots showing the variation of the rate constant (k) with temperature (T) are given below. The plot that
follows Arrhenius equation is
A) B)
K

K
T T
C) D)
K

T T

Sol. (A)
k = Ae− Ea / RT
As T ↑; k ↑ exponentially.
K

5. The species which by definition has ZERO standard molar enthalpy of formation at 298 K is
A) Br2 (g) B) Cl2 (g)
C) H2O (g) D) CH4 (g)

Sol. (B)
Cl2 is gas at 298 K while Br2 is a liquid.

6. The bond energy (in kcal mol – 1 ) of a C – C single bond is approximately

A) 1 B) 10
C) 100 D) 1000

Ans. (C)

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IITJEE2010-Paper 1-CMP-5

7. The correct structure of ethylenediaminetetraacetic acid (EDTA) is

A) HOOC CH2 CH2 COOH B) HOOC COOH
N CH CH N N CH2 CH2 N
CH2 COOH HOOC COOH
HOOC CH2
C) HOOC CH2 CH2 COOH D) COOH
N CH2 CH2 N
CH2 COOH CH2
HOOC CH2 H
HOOC CH2
NHC CH N
CH2 COOH
H CH2
HOOC

Ans. (C)

8. The ionization isomer of [Cr(H2O)4Cl(NO2)]Cl is

A) [Cr(H2O)4(O2N)]Cl2 B) [Cr(H2O)4Cl2](NO2)
C) [Cr(H2O)4Cl(ONO)]Cl D) [Cr(H2O)4Cl2(NO2)]H2O

Sol. (B)
Cl – is replaced by NO −2 in ionization sphere.

SECTION – II (Multiple Correct Choice Type)

This section contains 5 multiple choice questions. Each question has four choices A), B), C) and D) out of which
ONE OR MORE may be correct.

9. In the Newman projection for 2,2-dimethylbutane

X
H3C CH3

H H

Y
X and Y can respectively be
A) H and H B) H and C2H5
C) C2H5 and H D) CH3 and CH3

Sol. (B, D)
CH3

H3C CH2 C2 CH3

4 3 1
CH3
On C2 – C3 bond axis
X = CH3
Y = CH3
On C1 – C2 bond axis
X=H
Y = C2H5

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IITJEE2010-Paper 1-CMP-6

10. Aqueous solutions of HNO3, KOH, CH3COOH, and CH3COONa of identical concentrations are provided.
The pair (s) of solutions which form a buffer upon mixing is(are)
A) HNO3 and CH3COOH B) KOH and CH3COONa
C) HNO3 and CH3COONa D) CH3COOH and CH3COONa

Sol. (C, D)
In option (C), if HNO3 is present in limiting amount then this mixture will be a buffer. And the mixture
given in option (D), contains a weak acid (CH3COOH) and its salt with strong base NaOH, i.e.
CH3COONa.

OH

( ) 2
NaOH aq / Br
 →

11. In the reaction the intermediate(s) is(are)

A) O B) O

Br

Br Br
Br
C) O D) O

Br
Br

Sol. (A, B, C)
Phenoxide ion is para* and ortho directing. (* preferably)
O O O O O

→
Br2
←
→ →
Br2
←
→

Br Br Br
Br Br
O O O O

Br
+ 
→ +

Br Br
Br

12. The reagent(s) used for softening the temporary hardness of water is(are)
A) Ca3(PO4)2 B) Ca(OH)2
C) Na2CO3 D) NaOCl

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IITJEE2010-Paper 1-CMP-7

Sol. (B, C, D)
Ca ( HCO3 )2 + Ca ( OH )2 
→ 2CaCO3 ↓ +2H 2 O
[Clarke 's method ]
NaOCl + H 2 O HOCl + NaOH
− −
→ CO32 − + H 2 O
OH + HCO  3

Ca ( HCO3 )2 + Na 2 CO3 
→ CaCO3 ↓ +2NaHCO3

13. Among the following, the intensive property is (properties are)

A) molar conductivity B) electromotive force
C) resistance D) heat capacity

Sol. (A, B)
Resistance and heat capacity are mass dependent properties, hence extensive.

SECTION-III (Paragraph Type)

This section contains 2 paragraphs. Based upon the first paragraph 2 multiple choice questions and based upon the
second paragraph 3 multiple choice questions have to be answered. Each of these questions has four choices A),
B), C) and D) out of WHICH ONLY ONE CORRECT.

Paragraph for Question Nos. 14 to 15

The concentration of potassium ions inside a biological cell is at least twenty times higher than the outside. The
resulting potential difference across the cell is important in several processes such as transmission of nerve impulses
and maintaining the ion balance. A simple model for such a concentration cell involving a metal M is:
M(s) M+(aq; 0.05 molar)M+(aq), 1 molar)M(s)
For the above electrolytic cell the magnitude of the cell potential Ecell= 70 mV.

14. For the above cell

A) E cell < 0; ∆G > 0 B) E cell > 0; ∆G < 0
C) E cell < 0; ∆G > 0 o
D) E cell > 0; ∆G o > 0
Sol. (B)
M ( s ) + M (+aq )1M 
→ M (+aq ).05 M + M ( s )
According to Nernst equation ,
+
2.303RT M.05 M
Ecell = 0 - log +
F M1M
2.303RT
=0- log ( 5 × 10−2 )
F
= +ve
Hence, |Ecell | = Ecell = 0.70 V and ∆G < 0 for the feasibility of the reaction.

15. If the 0.05 molar solution of M+ is replaced by 0.0025 molar M+ solution, then the magnitude of the cell
potential would be
A) 35 mV B) 70 mV
C) 140 mV D) 700 mV

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IITJEE2010-Paper 1-CMP-8

Sol. (C)
2.303RT
From above equation = 0.0538
F
0.0538
So, Ecell = E ocell − log 0.0025
1
0.0538
=0 − log 0.0025
1
≈ 0.13988 V
≈ 140 mV

Paragraph for Question Nos. 16 to 18

Copper is the most noble of the first row transition metals and occurs in small deposits in several countries. Ores of
copper include chalcanthite ( CuSO 4 ⋅ 5H 2 O ) , atacamite ( Cu 2 Cl ( OH )3 ) , cuprite ( Cu 2 O ) , copper glance ( Cu 2S )
and malachite ( Cu 2 ( OH )2 CO3 ) . However, 80% of the world copper production comes from the ore of chalcopyrite
( CuFeS2 ) . The extraction of copper from chalcopyrite involves partial roasting, removal of iron and self-reduction.
16. Partial roasting of chalcopyrite produces
A) Cu2S and FeO B) Cu2O and FeO
C) CuS and Fe2O3 D) Cu2O and Fe2O3

Sol. (B)
2CuFeS2 + O 2 → Cu 2S + 2FeS + SO 2 ↑
2Cu 2S + 3O 2 → 2Cu 2 O + 2SO 2 ↑
2FeS + 3O 2 → 2FeO + 2SO 2 ↑

17. Iron is removed from chalcopyrite as

A) FeO B) FeS
C) Fe2O3 D) FeSiO3

Sol. (D)
FeO + SiO 2 → FeSiO3
( slag )

18. In self-reduction, the reducing species is

A) S B) O2−
C) S2− D) SO2

Sol. (C)
Cu 2S + 2Cu 2 O → 6Cu + SO 2 ↑
( Blister copper )
S2 − → S4+ is oxidation, i.e., S2− is reducing agent.

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IITJEE2010-Paper 1-CMP-9

SECTION-IV (Integer Type)

This section contains TEN questions. The answer to each question is a single digit integer ranging from 0 to 9. The
correct digit below the question number in the ORS is to be bubbled.

19. A student performs a titration with different burettes and finds titre values of 25.2 mL, 25.25 mL and 25.0
mL. The number of significant figures in the average titre value is

Ans. 3

20. The concentration of R in the reaction R → P was measured as a function of time and the following data is
obtained:
[R] (molar) 1.0 0.75 0.40 0.10
t (min.) 0.0 0.05 0.12 0.18
The order of the reaction is

Sol. 0
From two data, (for zero order kinetics)
x 0.25
KI = = =5
t 0.05
x 0.60
K II = = =5
t 0.12

235 142 90
21. The number of neutrons emitted when 92 U undergoes controlled nuclear fission to 54 Xe and 38 Sr is
Sol. 3
92 U 235 →54 Xe142 + 38 Sr 90 + 30 n1

22. The total number of basic groups in the following form of lysine is
H3 N CH2 CH2 CH2 CH2 O

CH C

H2N O

Sol. 2
O

C O and NH2 are basic groups in lysine.

23. The total number of cyclic isomers possible for a hydrocarbon with the molecular formula C4H6 is

Sol. 5
In C4H6, possible cyclic isomers are

, , , ,

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IITJEE2010-Paper 1-CMP-10

24. In the scheme given below, the total number of intra molecular aldol condensation products formed from
‘Y’ is

( )
1. NaOH aq

1. O3
2. Zn, H 2 O
→ Y 
2. heat
→

Sol. 1
O
O

( )
1. NaOH aq

1. O3
2.Zn, H 2 O
→ 
2. heat
→

25. Amongst the following, the total number of compound soluble in aqueous NaOH is
H3C CH3
OH
N COOH OCH2 CH3

CH2 OH

NO2 OH CH2 CH3 COOH

CH2CH3

N
H3C CH3

Sol. 4
COOH OH OH COOH

N
H3C CH3
These four are soluble in aqueous NaOH.

26. Amongst the following, the total number of compounds whose aqueous solution turns red litmus paper blue
is
KCN K2SO4 (NH4)2C2O4 NaCl Zn(NO3)2 FeCl3 K2CO3 NH4NO3 LiCN

Sol. 3
KCN, K2CO3, LiCN are basic in nature and their aqueous solution turns red litmus paper blue.

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IITJEE2010-Paper 1-CMP-11

27. Based on VSEPR theory, the number of 90 degree F−Br−F angles in BrF5 is

Sol. 0

Br
F F

F F
F
All four planar bonds (F−Br−F) will reduce from 90o to 84.8o after p − bp repulsion.

28. The value of n in the molecular formula BenAl2Si6O18 is

Sol. 3
Be3Al2Si6O18 (Beryl)
(according to charge balance in a molecule)
2n + 6 + 24 − 36 = 0
n=3

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IITJEE2010-Paper 1-CMP-12

PART - II: MATHEMATICS

SECTION – I (Single Correct Choice Type)

This Section contains 8 multiple choice questions. Each question has four choices A), B), C) and D) out of which
ONLY ONE is correct.

29. Let ω be a complex cube root of unity with ω ≠ 1. A fair die is thrown three times. If r1, r2 and r3 are the
numbers obtained on the die, then the probability that ωr1 + ωr2 + ωr3 = 0 is
1 1
(A) (B)
18 9
2 1
(C) (D)
9 36

Sol. (C)
r1, r2, r3 ∈ {1, 2, 3, 4, 5, 6}
r1, r2, r3 are of the form 3k, 3k + 1, 3k + 2
3! × 2 C1 × 2 C1 × 2 C1 6 × 8 2
Required probability = = = .
6× 6× 6 216 9

30. Let P, Q, R and S be the points on the plane with position vectors −2ˆi − ˆj, 4ˆi, 3ˆi + 3ˆj and −3ˆi + 2ˆj
respectively. The quadrilateral PQRS must be a
(A) parallelogram, which is neither a rhombus nor a rectangle
(B) square
(C) rectangle, but not a square
(D) rhombus, but not a square

Sol. (A) S ( −3iˆ + 2ˆj) R (3iˆ + 3ˆj)

Evaluating midpoint of PR and QS which
 ˆi 
gives M ≡  + ˆj , same for both.
2 
PQ = SR = 6ˆi + ˆj M

PS = QR = −ˆi + 3ˆj
P ( −2iˆ − ˆj) ˆ
Q (4i)
⇒ PQ ⋅ PS ≠ 0
PQ || SR, PS || QR and PQ = SR , PS = QR
Hence, PQRS is a parallelogram but not rhombus or rectangle.
 x  1 
31. The number of 3 × 3 matrices A whose entries are either 0 or 1 and for which the system A  y  = 0  has
 z  0 
exactly two distinct solutions, is
(A) 0 (B) 29 − 1
(C) 168 (D) 2

Sol. (A)
Three planes cannot intersect at two distinct points.

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IITJEE2010-Paper 1-CMP-13

x
1 t ln (1 + t )
32. The value of lim
x →0 x 3 ∫
0
t4 + 4
dt is

1
(A) 0 (B)
12
1 1
(C) (D)
24 64

Sol. (B)
x
1 t ln (1 + t ) dt x ln (1 + x )
lim
x →0 x 3 ∫
0
t +44
= lim
x →0 ( x 4 + 4 ) 3x 2
1 ln (1 + x ) 1
= lim = .
x →0 3 x ( x + 4 )
4 12

33. Let p and q be real numbers such that p ≠ 0, p3 ≠ q and p3 ≠ − q. If α and β are nonzero complex numbers
α β
satisfying α + β = − p and α3 + β3 = q, then a quadratic equation having and as its roots is
β α
(A) ( p3 + q ) x 2 − ( p3 + 2q ) x + ( p3 + q ) = 0 (B) ( p3 + q ) x 2 − ( p3 − 2q ) x + ( p3 + q ) = 0
(C) ( p3 − q ) x 2 − ( 5p3 − 2q ) x + ( p3 − q ) = 0 (D) ( p3 − q ) x 2 − ( 5p3 + 2q ) x + ( p3 − q ) = 0

Sol. (B)
α3 + β3 = q
⇒ (α + β)3 − 3αβ (α + β) = q
q + p3
⇒ − p3 + 3pαβ = q ⇒ αβ =
3p
α β α β
x2 −  +  x + ⋅ = 0
β α β α

x2 −
( α 2 + β2 ) x + 1 = 0
αβ
 ( α + β )2 − 2αβ 
⇒ x 2 −   x + 1 = 0
 αβ 
 3
p +q 
p2 − 2  
⇒ x2 −  3p  x + 1 = 0
p3 + q
3p
⇒ (p3 + q) x2 − (3p3 − 2p3 − 2q) x + (p3 + q) = 0
⇒ (p3 + q) x2 − (p3 − 2q) x + (p3 + q) = 0.

2 2
34. Let f, g and h be real-valued functions defined on the interval [0, 1] by f ( x ) = e x + e − x , g ( x )
2 2 2 2
= xe x + e − x and h (x) = x 2 e x + e − x . If a, b and c denote, respectively, the absolute maximum of f, g and
h on [0, 1], then
(A) a = b and c ≠ b (B) a = c and a ≠ b
(C) a ≠ b and c ≠ b (D) a = b = c

Sol. (D)

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IITJEE2010-Paper 1-CMP-14

f(x) = e x + e − x ⇒ f′(x) = 2x ( e x − e − x ) ≥ 0 ∀ x ∈ [0, 1]

2 2 2 2

Clearly for 0 ≤ x ≤ 1 f(x) ≥ g(x) ≥ h(x)

1
∵ f(1) = g(1) = h(1) = e + and f(1) is the greatest
e
1
∴ a = b = c = e + ⇒ a = b = c.
e

35. If the angles A, B and C of a triangle are in an arithmetic progression and if a, b and c denote the lengths of
a c
the sides opposite to A, B and C respectively, then the value of the expression sin 2C + sin 2A is
c a
1 3
(A) (B)
2 2
(C) 1 (D) 3

Sol. (D)
B = 60°
a c
∴ sin2C + sin2A = 2sinA cosC + 2sinCcosA
c a
3
= 2sin(A + C) = 2sinB = 2 × = 3.
2

x y z
36. Equation of the plane containing the straight line = = and perpendicular to the plane containing the
2 3 4
x y z x y z
straight lines = = and = = is
3 4 2 4 2 3
(A) x + 2y − 2z = 0 (B) 3x + 2y − 2z = 0
(C) x − 2y + z = 0 (D) 5x + 2y − 4z = 0

Sol. (C)
x y z
Plane 1: ax + by + cz = 0 contains line = =
2 3 4
∴ 2a + 3b + 4c = 0 …(i)
x y z x y z
Plane 2: a′x + b′y + c′z = 0 is perpendicular to plane containing lines = = and = =
3 4 2 4 2 3
∴ 3a′ + 4b′ + 2c′ = 0 and 4a′ + 2b′ + 3c′ = 0
a′ b′ c′
⇒ = =
12 − 4 8 − 9 6 − 16
⇒ 8a − b − 10c = 0 …(ii)
From (i) and (ii)
a b c
= =
−30 + 4 32 + 20 −2 − 24
⇒ Equation of plane x − 2y + z = 0.

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IITJEE2010-Paper 1-CMP-15

SECTION − II (Multiple Correct Choice Type)

This section contains 5 multiple choice questions. Each question has four choices A), B), C) and D) out of which
ONE OR MORE may be correct.

37. Let z1 and z2 be two distinct complex numbers and let z = (1 − t) z1 + tz2 for some real number t with 0 < t
< 1. If Arg (w) denotes the principal argument of a non-zero complex number w, then
(A) |z − z1| + |z − z2| = |z1 − z2| (B) Arg (z − z1) = Arg (z − z2)
z − z1 z − z1
(C) =0 (D) Arg (z − z1) = Arg (z2 − z1)
z 2 − z1 z2 − z1

Sol. (A), (C), (D)

Given z = (1 − t) z1 + tz2
z − z1  z − z1 
⇒ = t ⇒ arg  =0 … (1)
z 2 − z1  z 2 − z1 
⇒ arg (z − z1) = arg (z2 − z1)
z − z1 z − z1
=
z 2 − z1 z2 − z1
z − z1 z − z1
=0
z 2 − z1 z2 − z1
P(z)
A(z1) B(z2)
AP + PB = AB
⇒ |z − z1| + |z − z2| = |z1 − z2|.

1 4
x 4 (1 − x )
38. The value(s) of ∫
0
1 + x2
dx is (are)

22 2
(A) − π (B)
7 105
71 3π
(C) 0 (D) −
15 2

Sol. (A)
1
x 4 (1 − x) 4
∫
0
1 + x2
dx

1
 4 
∫  x
6
= − 4 x 5 + 5x 4 − 4 x 2 + 4 −  dx
2
0
1+ x 
1
 x 7 2x 6 4x 3 
=  − + x5 − + 4x  − π
7 3 3 0
1 2 4 22
= − +1− + 4 − π = −π
7 3 3 7

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IITJEE2010-Paper 1-CMP-16

π
39. Let ABC be a triangle such that ∠ACB = and let a, b and c denote the lengths of the sides opposite to A,
6
B and C respectively. The value(s) of x for which a = x2 + x + 1, b = x2 − 1 and c = 2x + 1 is (are)
(A) − ( 2 + 3 ) (B) 1 + 3
(C) 2 + 3 (D) 4 3

Sol. (B)
Using cosine rule for ∠C
3 ( x 2 + x + 1) + ( x 2 − 1) − ( 2x + 1)
2 2 2
=
2 2 ( x 2 + x + 1)( x 2 − 1)
2x 2 + 2 x − 1
⇒ 3=
x2 + x + 1
⇒ ( 3 − 2 ) x 2 + ( 3 − 2 ) x + ( 3 + 1) = 0
(2 − 3) ± 3
⇒x=
2 ( 3 − 2)
⇒ x = − (2 + 3) , 1 + 3 ⇒ x = 1 + 3 as (x > 0).

40. Let A and B be two distinct points on the parabola y2 = 4x. If the axis of the parabola touches a circle of
radius r having AB as its diameter, then the slope of the line joining A and B can be
1 1
(A) − (B)
r r
2 2
(C) (D) −
r r

Sol. (C), (D)

A = ( t12 , 2t1 ) , B = ( t 22 , 2t 2 )
 t2 + t2 
Centre =  1 2 , ( t1 + t 2 ) 
 2 
t1 + t2 = ± r
2(t − t ) 2 2
m = 21 22 = =± .
t1 − t 2 t1 + t 2 r

x
41. Let f be a real-valued function defined on the interval (0, ∞) by f ( x ) = ln x + ∫
0
1 + sin t dt . Then which of

the following statement(s) is (are) true?

(A) f ″(x) exists for all x ∈ (0, ∞)
(B) f′(x) exists for all x ∈ (0, ∞) and f′ is continuous on (0, ∞), but not differentiable on (0, ∞)
(C) there exists α > 1 such that |f′(x)| < |f(x)| for all x ∈ (α, ∞)
(D) there exists β > 0 such that |f(x)| + |f′(x)| ≤ β for all x ∈ (0, ∞)

Sol. (B), (C)

1
f ′(x ) = + 1 + sin x
x
π
f′(x) is not differentiable at sinx = −1 or x = 2 nπ − , n ∈ N
2
In x ∈ (1, ∞) f(x) > 0, f′(x) > 0

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IITJEE2010-Paper 1-CMP-17

Consider f(x) − f′(x)

x
1
= ln x + ∫
0
1 + sin t dt −
x
− 1 + sin x

 x  1
0
∫
=  1 + sin t dt − 1 + sin x  + ln x −
 

x
x
Consider g(x) = ∫
0
1 + sin t dt − 1 + sin x

It can be proved that g(x) ≥ 2 2 − 10 ∀ x ∈ (0, ∞)

1 1
Now there exists some α > 1 such that − ln x ≤ 2 2 − 10 for all x ∈ (α, ∞) as − lnx is strictly
x x
decreasing function.
1
⇒ g(x) ≥ − ln x .
x

SECTION − III (Paragraph Type)

This section contains 2 paragraphs. Based upon the first paragraph 2 multiple choice questions and based upon the
second paragraph 3 multiple choice questions have to be answered. Each of these questions has four choices A),
B), C) and D) out of WHICH ONLY ONE CORRECT.

Paragraph for Questions 42 to 43

x2 y2
The circle x2 + y2 − 8x = 0 and hyperbola − = 1 intersect at the points A and B.
9 4

42. Equation of a common tangent with positive slope to the circle as well as to the hyperbola is
(A) 2x − 5y − 20 = 0 (B) 2x − 5y + 4 = 0
(C) 3x − 4y + 8 = 0 (D) 4x − 3y + 4 = 0

Sol. (B)
x2 y2
A tangent to − = 1 is y = mx + 9m 2 − 4, m > 0
9 4
It is tangent to x2 + y2 − 8x = 0
4m + 9m 2 − 4
∴ =4
1+ m2
⇒ 495m4 + 104m2 − 400 = 0
4 2
⇒ m2 = or m =
5 5
2 4
∴ the tangent is y = m+
5 5
⇒ 2 x − 5y + 4 = 0 .

43. Equation of the circle with AB as its diameter is

(A) x2 + y2 − 12x + 24 = 0 (B) x2 + y2 + 12x + 24 = 0
(C) x2 + y2 + 24x − 12 = 0 (D) x2 + y2 − 24x − 12 = 0

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IITJEE2010-Paper 1-CMP-18

Sol. (A)
A point on hyperbola is (3secθ, 2tanθ)
It lies on the circle, so 9sec2θ + 4tan2θ − 24secθ = 0
2
⇒ 13sec2θ − 24secθ − 4 = 0 ⇒ secθ = 2, −
13
∴ secθ = 2 ⇒ tanθ = 3 .
The point of intersection are A ( 6, 2 3 ) and B ( 6, − 2 3 )
∴ The circle with AB as diameter is
(x − 6)2 + y2 = ( 2 3 )
2
⇒ x2 + y2 − 12x + 24 = 0.

Paragraph for Questions 44 to 46

Let p be an odd prime number and Tp be the following set of 2 × 2 matrices :

 a b  
Tp = A =   : a, b, c ∈ {0, 1, .... , p − 1}
 c a  

44. The number of A in Tp such that A is either symmetric or skew-symmetric or both, and det(A) divisible by
p is
(A) (p − 1)2 (B) 2(p − 1)
(C) (p − 1)2 + 1 (D) 2p − 1

Sol. (D)
We must have a2 − b2 = kp
⇒ (a + b) (a − b) = kp
⇒ either a − b = 0 or a + b is a multiple of p
when a = b; number of matrices is p
and when a + b = multiple of p ⇒ a, b has p − 1
∴ Total number of matrices = p + p − 1
= 2p − 1.

45. The number of A in Tp such that the trace of A is not divisible by p but det (A) is divisible by p is
[Note: The trace of a matrix is the sum of its diagonal entries.]
(A) (p − 1) (p2 − p + 1) (B) p3 − (p − 1)2
2
(C) (p − 1) (D) (p − 1) (p2 − 2)

Ans. (C)

46. The number of A in Tp such that det (A) is not divisible by p is

(A) 2p2 (B) p3 − 5p
3
(C) p − 3p (D) p3 − p2

Ans. (D)

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IITJEE2010-Paper 1-CMP-19

SECTION − IV (Integer Type)

This section contains TEN questions. The answer to each question is a single digit integer ranging from 0 to 9. The
correct digit below the question number in the ORS is to be bubbled.

k −1
47. Let Sk, k = 1, 2, ….. , 100, denote the sum of the infinite geometric series whose first term is and the
k!
100
1 1002
common ratio is
k
. Then the value of + ∑
100! k =1
( k 2 − 3k + 1) Sk is

Sol. (3)
k −1
1
Sk = k ! =
1 ( k − 1)!
1−
k
100
1
∑ (k
k =2
2
− 3k + 1)
( k − 1)!
100
( k − 1) 2 − k
= ∑
k =2
( k − 1)!
k −1
∑ (k − 2)! − (k − 1)!
k
=

2 3 3 4
= − + − + ⋅⋅⋅
1! 2! 2! 3!
2 1 2 3 3 4 99 100
= − + − + − + ⋅⋅⋅ + −
1! 0! 1! 2! 2! 3! 98! 99!
100
=3− .
99!

48. The number of all possible values of θ, where 0 < θ < π, for which the system of equations
(y + z) cos 3θ = (xyz) sin 3θ
2 cos 3θ 2sin 3θ
x sin 3θ = +
y z
(xyz) sin 3θ = (y + 2z) cos 3θ + y sin 3θ
have a solution (x0, y0, z0) with y0z0 ≠ 0, is

Sol. (3)
(y + z) cos 3θ − (xyz) sin 3θ = 0 … (1)
xyz sin 3θ = (2 cos 3θ) z + (2 sin 3θ) y … (2)
∴ (y + z) cos 3θ = (2 cos 3θ) z + (2 sin 3θ) y = (y + 2z) cos 3θ + y sin 3θ
y (cos 3θ − 2 sin 3θ) = z cos 3θ and
y (sin 3θ − cos 3θ) = 0 ⇒ sin 3θ − cos 3θ = 0 ⇒ sin 3θ = cos 3θ
∴ 3θ = nπ + π/4

49. Let f be a real-valued differentiable function on R (the set of all real numbers) such that f(1) = 1. If the y-
intercept of the tangent at any point P(x, y) on the curve y = f(x) is equal to the cube of the abscissa of P,
then the value of f(−3) is equal to

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IITJEE2010-Paper 1-CMP-20

Sol. (9)
y – y1 = m(x – x1)
Put x = 0, to get y intercept
y1 – mx1 = x13
dy
y1 – x1 = x13
dx
dy
x − y = −x3
dx
dy y
− = −x 2
dx x
1
∫ − dx
e x = e − ln x =
1
x
1 1
y×
x ∫
= − x 2 × dx
x
x2
∫
y y
= − xdx ⇒ = − + c
x x 2
x3 3
⇒ f(x) = − + x ∴ f(–3) = 9.
2 2

 π π nπ
50. The number of values of θ in the interval  − ,  such that θ ≠ for n = 0, ±1, ±2 and tanθ = cot 5θ as
 2 2 5
well as sin 2θ = cos 4θ is

Sol. (3)
tanθ = cot 5θ
⇒ cos 6θ = 0
4cos3 2θ − 3cos 2θ = 0
3
⇒ cos 2θ = 0 or ±
2
sin 2θ = cos 4θ
⇒ 2sin2 2θ + sin2θ − 1 = 0
2sin2 2θ + 2sin 2θ − sin2θ − 1 = 0
1
sin2θ = −1 or sin2θ =
2
cos2θ = 0 and sin2θ = −1
π π
⇒ 2θ = − ⇒θ=−
2 4
3 1
cos2θ = ± , sin2θ =
2 2
π 5π π 5π
⇒ 2θ = , ⇒θ= ,
6 6 12 12
π π 5π
∴ θ=− , ,
4 12 12

1
51. The maximum value of the expression is
sin θ + 3sin θ cos θ + 5cos 2 θ
2

Sol. (2)

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IITJEE2010-Paper 1-CMP-21

1
3
4 cos 2 θ + 1 + sin 2θ
2
1
⇒
3
2 [1 + cos 2θ] + 1 + sin 2θ
2
1 11
lies between to
2 2
∴ maximum value is 2.
Minimum value of 1 + 4 cos2 θ + 3 sin θ cos θ
4 (1 + cos 2θ ) 3
1+ + sin 2θ
2 2
3
= 1+ 2 + 2 cos 2θ + sin 2θ
2
3
= 3 + 2 cos 2θ + sin 2θ
2
9 5 1
∴ = 3 − 4+ = 3 − = .
4 2 2
1
So maximum value of is 2.
3
4 cos 2 θ + 1 + sin 2θ
2

ˆi − 2ˆj 2ˆi + ˆj + 3kˆ

52. If a and b are vectors in space given by a = and b = , then the value of
5 14
( 2a + b ) ⋅ ( a × b ) × ( a − 2b ) is

Sol. (5)
E = ( 2a + b ) ⋅  2 b a − 2 ( a ⋅ b ) b − ( a ⋅ b ) a + a b 
2 2

2−2
a⋅b = =0
70
a =1
|b| = 1
a⋅b = 0
E = ( 2a + b ) ⋅  2 b a + a b 
2 2

= 4a
2 2
b +a
2
(a ⋅ b) + 2 b 2 ( b ⋅ a ) + a 2 b 2
2 2
= 5a b =5

x2 y2
53. The line 2x + y = 1 is tangent to the hyperbola −
= 1 . If this line passes through the point of
a 2 b2
intersection of the nearest directrix and the x-axis, then the eccentricity of the hyperbola is

Sol. (2)
a 
Substituting  , 0  in y = − 2x + 1
e 
2a
0 = − +1
e

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IITJEE2010-Paper 1-CMP-22

2a
=1
e
e
a=
2
Also, 1 = a 2 m 2 − b 2
1 = a2m2 − b2
1 = 4a2 − b2
4e 2
1= − b2
4
b2 = e2 − 1.
Also, b2 = a2 (e2 − 1)
∴ a = 1, e = 2

x −1 y − 2 z − 3
54. If the distance between the plane Ax − 2y + z = d and the plane containing the lines = =
2 3 4
x −2 y −3 z−4
and = = is 6 , then |d| is
3 4 5

Sol. (6)
2l + 3m + 4n = 0
3l + 4m + 5n = 0
l m n
= =
−1 2 −1
Equation of plane will be
a (x − 1) + b (y − 2) + c (z − 3) = 0
− 1 (x − 1) + 2 (y − 2) − 1 (z − 3) = 0
− x + 1 + 2y − 4 − z + 3 = 0
− x + 2y − z = 0
x − 2y + z = 0
|d|
= 6
6
d = 6.

55. For any real number x, let |x| denote the largest integer less than or equal to x. Let f be a real valued
function defined on the interval [−10, 10] by
 x − [x] if [x ] is odd
f (x) = 
1 + [ x ] − x if [x ] is even
10
π2
Then the value of
10 ∫ f (x) cos πx dx is
−10

Sol. (4)
x − 1, 1 ≤ x < 2
f (x) = 
1 − x, 0 ≤ x < 1

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IITJEE2010-Paper 1-CMP-23

−2 −1 1 2 3

f(x) is periodic with period 2

10
∴I=
−10
∫ f (x) cos πx dx
10 2

∫
= 2 f (x) cos πx dx = 2 × 5 f (x ) cos πx dx
0
∫
0

1 2 
 0 ∫ 1
∫
= 10  (1 − x ) cos πx dx + ( x − 1) cos πx dx  = 10 ( I1 + I 2 )

2

∫
I 2 = ( x − 1) cos πx dx put x − 1 = t
1
1

∫
I 2 = − t cos πt dt
0
1 1

∫
I1 = (1 − x ) cos πx dx = − x cos ( πx ) dx
0
∫
0

 1 
 0 ∫
∴ I = 10  −2 x cos πx dx 

1
 sin πx cos πx 
= −20  x +
 π π2  0
 1 1  40 π2
= −20  − 2 − 2  = 2 ∴ I=4
 π π  π 10

2π 2π
56. Let ω be the complex number cos + i sin . Then the number of distinct complex numbers z satisfying
3 3
z +1 ω ω2
ω z + ω2 1 = 0 is equal to
ω2 1 z+ω

Sol. (1)
ω = e i 2π / 3
z +1 ω ω2
ω z + ω2 1 =0
2
ω 1 z+ω

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IITJEE2010-Paper 1-CMP-24

1 ω ω2
z 1 z + ω2 1 =0
1 1 z+ω
⇒ z ( z + ω2 ) ( z + ω) − 1 − ω ( z + ω − 1) + ω2 (1 − z − ω2 )  = 0
⇒ z3 = 0
⇒ z = 0 is only solution.

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IITJEE2010-Paper 1-CMP-25

PART - III: PHYSICS

SECTION – I (Single Correct Choice Type)

This Section contains 8 multiple choice questions. Each question has four choices A), B), C) and D) out of which
ONLY ONE is correct.

57. Incandescent bulbs are designed by keeping in mind that the resistance of their filament increases with the
increase in temperature. If at room temperature, 100 W, 60 W and 40 W bulbs have filament resistances
R100, R60 and R40, respectively, the relation between these resistances is
1 1 1
A) = + B) R100 = R40 + R60
R100 R 40 R 60
1 1 1
C) R100 > R60 > R40 D) > >
R100 R 60 R 40

Sol. (D)
Power ∝ 1/R

58. To Verify Ohm’s law, a student is provided with a test resistor RT, a high resistance R1, a small resistance
R2, two identical galvanometers G1 and G2, and a variable voltage source V. The correct circuit to carry out
the experiment is
A) G1 B) G1

R2 R1
G2 G2
RT R1 RT R2

V V
C) R1 D) R2
G1 G1

G2 G2
RT RT
R2 R1
V V

Sol. (C)
G1 is acting as voltmeter and G2 is acting as ammeter.

59. An AC voltage source of variable angular frequency ω and fixed amplitude V0 is connected in series with a
capacitance C and an electric bulb of resistance R (inductance zero). When ω is increased
A) the bulb glows dimmer B) the bulb glows brighter
C) total impedance of the circuit is unchanged D) total impedance of the circuit increases

Sol. (B)
1
Impedance Z = + R2
(ωC) 2
as ω increases, Z decreases.
Hence bulb will glow brighter

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IITJEE2010-Paper 1-CMP-26

60. A thin flexible wire of length L is connected to two adjacent fixed points and carries a current I in the
clockwise direction, as shown in the figure. When the system is put in a uniform magnetic field of strength
B going into the plane of the paper, the wire takes the shape of a circle. The tension in the wire is
××××××××
××××××××
××××××××
××××××××
××××××××
IBL
A) IBL B)
π
IBL IBL
C) D)
2π 4π

Sol. (C)
dθ T cos (dθ/2) T cos (dθ/2)
2T sin = BiRdθ
2
Tdθ = BiRdθ (for θ small) T T
BiL 2T sin (dθ/2)
T = BiR =
2π

61. A block of mass m is on an inclined plane of angle θ. The coefficient of

P
friction between the block and the plane is µ and tan θ > µ. The block is held
stationary by applying a force P parallel to the plane. The direction of force θ
pointing up the plane is taken to be positive. As P is varied from P1 =
mg(sinθ − µ cosθ) to P2 = mg(sinθ + µ cosθ), the frictional force f versus P
graph will look like
A) f B) f

P2
P1 P P1 P2 P

C) f D) f

P1 P1 P2
P2 P P

Sol. (A)
Initially the frictional force is upwards as P increases frictional force decreases.

62. A thin uniform annular disc (see figure) of P

mass M has outer radius 4R and inner radius
3R. The work required to take a unit mass 4R
from point P on its axis to infinity is
3R 4R

2GM 2GM
A) (4 2 − 5) B) − (4 2 − 5)
7R 7R
GM 2GM
C) B) ( 2 − 1)
4R 5R

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IITJEE2010-Paper 1-CMP-27

Sol. (A)
4R
σ2πrdrG
V=− ∫
3R r 2 + 16R 2
r dr

63. Consider a thin square sheet of side L and thickness t,

made of a material of resistivity ρ. The resistance
between two opposite faces, shown by the shaded areas t
in the figure is L
A) directly proportional to L B) directly proportional to t
C) independent of L D) independent of t

Sol. (C)
ρL
R=
Lt

64. A real gas behaves like an ideal gas if its

A) pressure and temperature are both high
B) pressure and temperature are both low
C) pressure is high and temperature is low
D) pressure is low and temperature is high

Sol. (D)

SECTION – II (Multiple Correct Choice Type)

This section contains 5 multiple choice questions. Each question has four choices A), B), C) and D) out of which
ONE OR MORE may be correct.

65. A point mass of 1 kg collides elastically with a stationary point mass of 5 kg. After their collision, the 1 kg
mass reverses its direction and moves with a speed of 2 ms−1. Which of the following statement(s) is (are)
correct for the system of these two masses?
A) Total momentum of the system is 3 kg ms−1
B) Momentum of 5 kg mass after collision is 4 kg ms−1
C) Kinetic energy of the centre of mass is 0.75 J
D) Total kinetic energy of the system is 4J

Sol. (A, C)
By conservation of linear momentum 1 kg 5 kg 2 m/s 5 kg
u = 5v − 2 …(i) u v
By Newton’s experimental law of collision
before collision after collision
u=v+2 …(ii)
using (i) and (ii) we have
v = 1 m/s and u = 3 m/s
1 2
Kinetic energy of the centre of mass = msystem vcm = 0.75 J
2

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IITJEE2010-Paper 1-CMP-28

66. One mole of an ideal gas in initial state A undergoes a cyclic process V
ABCA, as shown in the figure. Its pressure at A is P0. Choose the B
4V0
correct option(s) from the following
A) Internal energies at A and B are the same
V0 C A
B) Work done by the gas in process AB is P0V0 n 4
P0 T0 T
C) Pressure at C is
4
T0
D) Temperature at C is
4
Sol. (A, B)
Process AB is isothermal process

67. A student uses a simple pendulum of exactly 1m length to determine g, the acceleration due to gravity. He
uses a stop watch with the least count of 1 sec for this and records 40 seconds for 20 oscillations. For this
observation, which of the following statement(s) is (are) true?
A) Error ∆T in measuring T, the time period, is 0.05 seconds
B) Error ∆T in measuring T, the time period, is 1 second
C) Percentage error in the determination of g is 5%
D) Percentage error in the determination of g is 2.5%

Sol. (A, C)
∆T ∆ t 1
= =
T t 40
∆T = 0.05 sec
4π2 Ln 2
g=
t2
∆g 2∆t
=
g t
2 ∆t
⇒ % error = × 100 = 5%
t

68. A few electric field lines for a system of two charges Q1 and Q2 fixed
at two different points on the x-axis are shown in the figure. These
lines suggest that
A) Q1 > Q 2
Q1 Q2
B) Q1 < Q 2
C) at a finite distance to the left of Q1 the electric field is zero
D) at a finite distance to the right of Q2 the electric field is zero

Sol. (A, D)
No. of electric field lines of forces emerging from Q1 are larger than terminating at Q2

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69. A ray OP of monochromatic light is incident on the face AB of prism B

ABCD near vertex B at an incident angle of 60° (see figure). If the O 60°
refractive index of the material of the prism is 3 , which of the
following is (are) correct? P
C
A) The ray gets totally internally reflected at face CD 135°
B) The ray comes out through face AD
C) The angle between the incident ray and the emergent ray is 90° 90° 75°
D) The angle between the incident ray and the emergent ray is 120° A D

Sol. (A, B, C)
Using snell’s law B
1 1
sin −1 < sin −1 O 60° 135°
3 2
Net deviation is 90° P
C
45°
90° 30° 75°
A D

SECTION –III (Paragraph Type)

This section contains 2 paragraphs. Based upon the first paragraph 2 multiple choice questions and based upon the
second paragraph 3 multiple choice questions have to be answered. Each of these questions has four choices A),
B), C) and D) out of WHICH ONLY ONE CORRECT.

Paragraph for Questions 70 to 71

Electrical resistance of certain materials, known as superconductors, changes abruptly TC (B)

from a nonzero value to zero as their temperature is lowered below a critical
TC (0)
temperature Tc(0). An interesting property of superconductors is that their critical
temperature becomes smaller than Tc(0) if they are placed in a magnetic field, i.e., the
critical temperature Tc (B) is a function of the magnetic field strength B. The
dependence of Tc(B) on B is shown in the figure.
O B

70. In the graphs below, the resistance R of a superconductor is shown as a function of its temperature T for
two different magnetic fields B1 (solid line) and B2 (dashed line). If B2 is larger than B1 which of the
following graphs shows the correct variation of R with T in these fields?
A) R B2
B) R

B2 B1
B1
O T
O T

C) R D) R B1

B1 B2 B2

O T O T

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Sol. (A)
Larger the magnetic field smaller the critical temperature.

71. A superconductor has TC (0) = 100 K. When a magnetic field of 7.5 Tesla is applied, its Tc decreases to
75 K. For this material one can definitely say that when
A) B = 5 Tesla, Tc (B) = 80 K B) B = 5 Tesla, 75 K < Tc (B) < 100 K
C) B = 10 Tesla, 75K < Tc < 100 K D) B = 10 Tesla, Tc = 70K

Sol. (B)

Paragraph for Questions 72 to 74

When a particle of mass m moves on the x-axis in a potential V(x)

of the form V(x) = kx2 it performs simple harmonic motion.
m
The corresponding time period is proportional to , as can V0
k
be seen easily using dimensional analysis. However, the
motion of a particle can be periodic even when its potential
x
energy increases on both sides of x = 0 in a way different X0
from kx2 and its total energy is such that the particle does not
escape to infinity. Consider a particle of mass m moving on
the x-axis. Its potential energy is V(x) = αx4 (α > 0) for |x|
near the origin and becomes a constant equal to V0 for
|x| ≥ X0 (see figure).
72. If the total energy of the particle is E, it will perform periodic motion only if
A) E < 0 B) E > 0
C) V0 > E > 0 D) E > V0

Sol. (C)
Energy must be less than V0

73. For periodic motion of small amplitude A, the time period T of this particle is proportional to
m 1 m
A) A B)
α A α
α α
C) A D) A
m m

Sol. (B)
[α] = ML-2T-2
Only (B) option has dimension of time
Alternatively
2
1  dx 
m   + kx 4 = kA 4
2  dt 
2
 dx 
  =
dt
 
2k 4
m
A − x4 ( )
m A dx
4
2k ∫
0
A4 − x 4
= ∫ dt = T

m 1 1 du
4
2k A ∫ 0
1− u4
=T Substitute x = Au

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74. The acceleration of this particle for |x| > X0 is

V0
A) proportional to V0 B) proportional to
mX 0
V0
C) proportional to D) zero
mX 0

Sol. (D)
As potential energy is constant for |x| > X0, the force on the particle is zero hence acceleration is zero.

SECTION –IV (Integer Type)

This section contains TEN questions. The answer to each question is a single digit integer ranging from 0 to 9. The
correct digit below the question number in the ORS is to be bubbled.

6
75. Gravitational acceleration on the surface of a planet is g, where g is the gravitational acceleration on
11
2
the surface of the earth. The average mass density of the planet is times that of the earth. If the escape
3
-1
speed on the surface of the earth is taken to be 11 kms , the escape speed on the surface of the planet in
kms-1 will be

Sol. 3
g′ 6 ρ′ 2
= ; =
g 11 ρ 3
R′ 3 6
Hence, =
R 22
v′esc R ′ 2 ρ′ 3
∝ =
v esc R ρ 2
11
v′esc = 3 km/s.

76. A piece of ice (heat capacity = 2100 J kg-1 °C-1 and latent heat = 3.36 ×105J kg-1) of mass m grams is at
-5°C at atmospheric pressure. It is given 420 J of heat so that the ice starts melting. Finally when the
ice-water mixture is in equilibrium, it is found that 1 gm of ice has melted. Assuming there is no other heat
exchange in the process, the value of m is

Sol. 8
420 = (m × 2100 × 5 + 1 × 3.36 × 105 ) × 10−3
where m is in gm.

77. A stationary source is emitting sound at a fixed frequency f0, which is reflected by two cars approaching the
source. The difference between the frequencies of sound reflected from the cars is 1.2% of f0. What is the
difference in the speeds of the cars (in km per hour) to the nearest integer ? The cars are moving at constant
speeds much smaller than the speed of sound which is 330 ms-1.

Sol. 7
c+v
fapp = f0
c−v

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IITJEE2010-Paper 1-CMP-32

2f 0 c
df = dv
(c − v) 2
where c is speed of sound
1.2
df = f0
100
hence dv ≈ 7 km/hr.

78. The focal length of a thin biconvex lens is 20 cm. When an object is moved from a distance of 25 cm in
m
front of it to 50 cm, the magnification of its image changes from m25 to m50. The ratio 25 is
m50

Sol. 6
f
m=
f +u

79. An α- particle and a proton are accelerated from rest by a potential difference of 100 V. After this, their de
λp
Broglie wavelengths are λα and λp respectively. The ratio , to the nearest integer, is
λα

Sol. 3
1
mv 2 = qV
2
h
λ=
mv
λ= 8 3.

80. When two identical batteries of internal resistance 1Ω each are connected in series across a resistor R, the
rate of heat produced in R is J1. When the same batteries are connected in parallel across R, the rate is J2.
If J1 = 2.25 J2 then the value of R in Ω is

Sol. 4
2
 2E 
J1 =   R
R+2
2
 E 
J2 =   R since J1/J2 = 2.25
 R + 1/ 2 
R = 4 Ω.

81. Two spherical bodies A (radius 6 cm ) and B(radius 18 cm ) are at temperature T1 and T2, respectively.
The maximum intensity in the emission spectrum of A is at 500 nm and in that of B is at 1500 nm.
Considering them to be black bodies, what will be the ratio of the rate of total energy radiated by A to that
of B?

Sol. 9

λmT = constant
λATA = λBTB
Rate of total energy radiated ∝ AT4

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IITJEE2010-Paper 1-CMP-33

 π
82. When two progressive waves y1 = 4 sin(2x - 6t) and y2 = 3sin  2x − 6t −  are superimposed, the
 2
amplitude of the resultant wave is

Sol. 5
Two waves have phase difference π/2. 5
3

83. A 0.1 kg mass is suspended from a wire of negligible mass. The length of the wire is 1m and its cross-
sectional area is 4.9 × 10-7 m2. If the mass is pulled a little in the vertically downward direction and
released, it performs simple harmonic motion of angular frequency 140 rad s−1. If the Young’s modulus of
the material of the wire is n × 109 Nm-2, the value of n is

Sol. 4
YA
ω=
mL

84. A binary star consists of two stars A (mass 2.2Ms) and B (mass 11Ms), where Ms is the mass of the sun.
They are separated by distance d and are rotating about their centre of mass, which is stationary. The ratio
of the total angular momentum of the binary star to the angular momentum of star B about the centre of
mass is

Sol. 6
L total m1r12
= +1
LB m 2 r22
*******

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