This PDF is the Sample PDF taken from our

Comprehensive Study Material for NEET &

AIIMS

To purchase the books, go through the link below-

http://www.etoosindia.com/smartmall/bookList.do

ETOOS Comprehensive Study Material

For NEET & AIIMS
LAW OF MOTION &
CHAPTER
04
FRICTION
All that science can achieve is a perfect knowledge and a perfect un-
derstanding of the action of natural and moral forces.

“HERMANNVON HELMHOLTZ”

INTRODUCTION

T
hen we look around us, we find the planets moving around the sun in orderly manner,
movement of machinery parts in a factory, phases of the moon-all of them are following
certain laws. They all are acted upon by certain forces. In the preceding two chapters,
we described motion in terms of displacement, velocity and acceleration, i.e., we
used kinematic quantities for describing motion without considering what might
cause that motion. In order to understant this beauty, let us take a step forward by
understanging ''Force and laws of motion''. In this chapter, we shall study about force
and its effects on the objects and various alws related to motion of the objects.
 LAW OF MOTION & FRICTION

Inertial frame of Reference

The first law requires a frame of reference in which only the forces acting on a body can be responsible for any
acceleration produced in the body and not the acceleration of the frame of reference. These frames of reference are
known as inertial frames

2. The Second Law of motion

The rate of change in momentum of a body is equal to, and occurs in the direction of the net applied force. A body

of mass m in translational motion with velocity v , if acted upon with a net external force F , the second law
suggests:
 d 
F   mv 
dt
 
If mass of the body is constant, the above equation relates the acceleration a of the body with the net force F
acting on it
 d  
F   mv   ma
dt
The first law provides concept of force and the second law provides the quantitative definition of force, therefore
the second law is also valid only in inertial frames.
SI unit of force in newton. It is abbreviated as N. One newton equals to one kilogram-meter per second square
1 N = 1 kg-m/s2
–2
Dimension of force are [MLT ]

ETOOS KEY POINTS

(i) The second law is obviously consistent with the first law as F = 0 Implies a = 0
(ii) The second law of motion is a vector law it is actually a combination of three equations
dp x dp y
Fx   ma x , Fy   ma y
dt dt

dp z
Fz   ma z
dt
This means that if a force is not parallel to the velocity of the body, but makes some angles with it, it changes only
the component of velocity along the direction of force. The component of velocity normal to the force remains
unchanged.
(iii) The second law of motion given above is strictly applicable to a single point mass the force F in the law stand for
the net external force on the particle and a stands for the acceleration of the particle. Any internal forces in the
system are not to be include in F.
(iv) The second law of motion is a local relation what this means is that the force F at a point in space (location of the
particle) at a certain instant of time is related to a at the same point at the same instant that is acceleration here
and now is determined by the force here and now not by any history of the motion of the particle.

3. Newton Third Law of motion

Force is always a two-body interaction. The first law describes qualitatively and the second law describes
quantitatively what happens to a body if a force acts on it, but do not reveal anything about what happens to the
other body participating in the interaction responsible for the force.
The third law accounts for this aspect of the force and states the every action on a body has equal and opposite
reaction on the other body participating in the interaction.

6 etoosindia.com
Study with Best Etoos Faculties of Kota
IIT-JEE | PRE-MEDICAL | CBSE | FOUNDATION
PHYSICS FOR NEET & AIIMS

NEWTON’S LAW OF MOTION

I. Impulse - Momentum theorem

Impulse of a force is equal to the change of momentum Ft  p

1. Newton`s third law of motion :

Whenever a particle A exerts a force on another particle B, B simultaneously exerts a force on A with the same
magnitude in the opposite direction.

2. Spring Force (According to Hooke`s law) : Natural length

In equilibrium F = kx (k is spring constant)
F
Note : Spring force is non impulsive in nature. x

3. Motion of bodies in contact

When two bodies of masses m1 and m2 are kept on the frictionless surface and a force F is applied on one body,
then the force with which one body presses the other at the point of contact is called force of contact. These two
bodies will move with same acceleration a.

(a) When the force F acts on the body with mass m1 as shown in fig (i)
F = (m1 + m2)a

(b) If the force exerted by m2 on m1 is f1 (force of contact) then for body m1 : (F – f1) = m1a

m2F
For body m2 : f1 = m2a  action of m1 on m2 :
m1  m 2
4. Pulley system
A single fixed pulley changes the direction of force only and in general, assumed to be massless and frictionless.

5. SOME CASES OF PULLEY

Case I
Let m1 > m2
now for mass m1, m1g – T = m1a
for mass m2, T – m2g = m2a

 m1  m2  net pulling force

Acceleration = a = g=
 m1  m2  total mass to be pulled

44 etoosindia.com
India’s No. 1 Online Coaching Institute
IIT-JEE | PRE-MEDICAL | CBSE | FOUNDATION
 LAW OF MOTION & FRICTION

SOLVED EXAMPLE
Ex.1 With what acceleration ‘a’ shown the elevator 120  80
Sol. FBD of 8 kg block a   5m / s 2
descends so that the block of mass M exerts a force 8
Mg
of on the weighing machine ? [g = acceleration 120
10
due to gravity]
a

8g

Ex.3 As shown in figure, the left block rests on a table at

distance  from the edge while the right block is
kept at the same level so that thread is unstretched
and does not sag and then released. What will
happen first ?
(A) 0.3 g (B) 0.1 g
(C) 0.9g (D) 0.6 g
Sol. FBD of block :
Mg
Mg – N = Ma ; Now according to question N 
10
Mg
Mg 
So a  10  0.9g
M (A) Left block reach the edge of the table
N
(B) Right block hit the table
(C) Both (A) and (B) happens at the same time
a
(D) Can’t say anything
Sol. Net force in horizontal direction is more for left block
Mg so it will reach the edge of the table first.

Ex.4 The force exerted by the floor of an elevator on the

Ex.2 If the string is pulled down with a force of 120 N as foot of a person standing there is less than the
shown in the figure, then the acceleration of 8 kg weight of the person if the elevator is
block would
(A ) going up and slowing down
(B) going up and speeding up
(C) going down and slowing down
(D) going down and speeding up
Ans (A, D)
Sol. If N < mg then N = m(g-a)  elevator is going down
with acceleration or elevator is going up with
retardation.

(A) 10 m/s2 (B) 5 m/s2

(C) 0 m/s2 (D) 4 m/s2

48 etoosindia.com
Study with Best Etoos Faculties of Kota
IIT-JEE | PRE-MEDICAL | CBSE | FOUNDATION
PHYSICS FOR NEET & AIIMS

Exercise # 1 SINGLE OBJECTIVE NEET LEVEL

1. A mass of 1 kg is suspended by a string A. Another 6. If a bullet of mass 5 gm moving with velocity

string C is connected to its lower end (see figure). If 100 m / sec. penetrates the wooden block upto 6 cm.
a sudden jerk is given to C, then Then the average force imposed by the bullet on
the block is
A (A) 8300 N (B) 417 N
(C) 830 N (D) Zero
1kg B 7. A body of mass 0.4 kg straight at origin at t = 0 with
a speed of 10m/s in the positive x-axis direction is
subjected to a constant force F = 8N towards
C
negative x-axis. Calculate the position of the particle
(A) The porition AB of the string will break after 25 seconds.
(B) The porition BC of the string will break (A) –6000 m (B) –8000 m
(C) None of the strings will break (C) +4000 m (D) +7000 m
(D) The mass will start rotating
8. The velocity of a body of mass 20 kg decreases
2. In the above question, if the string C is stretched from 20 m/s to 5 m/s in a distance of 100 m. Force on
slowly then the body is
(A) The portion AB of the string will break (A) –27.5 N (B) –47.5 N
(B) The porition BC of the string will break (C) –37.5 N (D) –67.5 N
(C) None of the strings will break
(D) None of the above 9. The mass of a lift is 2000 kg. When the tension in
the supporting cable is 28000 N, then its acceleration
3. A particle is moving with a constant speed along a is
staright line path. A force is not required to
(A) 30 ms–2 downwards (B) 4 ms–2 upwards
(A) Increase its speed –2
(C) 4 ms downwards (D) 14 ms–2 upwards
(B) Decrease the momentum
(C) Change the direction 10. A ball of mass 0.2 kg is thrown vertically upwards
(D) Keep it moving with uniform velocity by applying a force by hand. If the hand moves 0.2
m while applying the force and the ball goes upto
4. A man getting down a running bus falls forward
2m height further, find the magnitude of the force.
because
Consider g = 10 m/s2
(A) Due to inertia of rest, road is left behind and
(A) 16 N (B) 20 N
man reaches forward
(B) Due to inertia of motion upper part of body (C) 22 N (D) 4 N
continues to be in motion in forward direction 11. Formula for true force is
while feet come to rest as soon as they touch
the road.
mdv
(A) F = ma (B) F 
(C) He leans forward as a matter of habbit. dt
dmv md 2 x
(D) Of the combined effect of all the three factors (C) F  (D) F 
stated in (A), (B) and (C) dt dt 2

5. When a bus suddenly takes a turn, the passangers 12. A body of mass 4 kg is accelerated upon by a
are thrown outwards because of constant force, travels a distance of 5 m in the first
(A) Inertia of direction second and a distance of 2 m in the third second.
The force acting on the body is
(B) Acceleration of motion
(C) Speed of motion (A) 6 N (B) 8 N
(D) Both (B) and (C) (C) 2 N (D) 4 N

etoosindia.com 55
India’s No. 1 Online Coaching Institute
IIT-JEE | PRE-MEDICAL | CBSE | FOUNDATION
 LAW OF MOTION & FRICTION

Exercise # 2 SINGLE OBJECTIVE AIIMS LEVEL

1. A monkey is descending from the branch of a tree In which situation impulse will be maximum
with constant acceleration. If the breaking strength
(A) I & II (B) III & I
of branch is 75% of the weight of the monkey, the
minimum acceleration with which the monkey can (C) III & IV (D) Only IV
slide down without breaking the branch is
3g 5. In the figure, the position–time graph of a particle
(A) g (B) of mass 0·1 kg is shown. The impulse at t=2 second
4
is
g g
(C) (D) (A) 0·2 kgms–1
4 2
2. A body of mass m1 exerts a force on another body (B) –0·2 kgms–1
of mass m2. If the magnitude of acceleration of m2 (C) 0·1 kgms–1
is a2, then the magnitude of the acceleration of m1 (D) –0·4 kgms–1
is (considering only two bodies in space)
m2a2
(A) Zero (B) m 6. A pulley is attached to the ceiling of a lift moving
1 upwards. Two particles are attached to the two
m1 a 2 ends of a string passing over the pulley. The
(C) (D) a2 masses of the particles are in the ratio 2 : 1. If the
m2
acceleration of the particles is g/2, then the
3. A trolley of mass 5 kg on a horizontal smooth acceleration of the lift will be
surface is pulled by a load of mass 2 kg by means
g
of uniform rope ABC of length 2 m and mass (A) g (B)
2
1 kg. As the load falls from BC = 0 to BC = 2m.
2
its acceleration in m/s changes– g g
20 20 (C) (D)
3 4
(A) to
6 5
20 30 7. A monkey is sitting on the pan of a spring balance
(B) to
8 8 which is placed on an elevator. The maximum
20 30 reading of the spring balance will be when :
(C) to
5 6 (A) the elevator is stationary
(D) None of the above
(B) the string of the elevator breaks and it drops
4. Figures I, II, III and IV depicts variation of force freely towards the earth
with time
(C) the elevator is accelerated downwards
(D) the elevator is accelerated upwards.

8. A body kept on a smooth inclined plane inclination

1 in x will remain stationary relative to the inclined
plane if the plane is given a horizontal acceleration
equal to :–

x2  1
(A) x 2  1g (B) g
x
gx g
(C) 2
(D)
x 1 x2  1

etoosindia.com 67
Study with Best Etoos Faculties of Kota
IIT-JEE | PRE-MEDICAL | CBSE | FOUNDATION
PHYSICS FOR NEET & AIIMS

Exercise # 3 PART - 1 MATRIX MATCH COLUMN

Following question contains statements given in two columns, which have to be matched. The statements in
Column-I are labelled as A, B, C and D while the statements in Column-II are labelled as p, q, r and s. Any given
statement in Column-I can have correct matching with one or more statement(s) in Column-II.
 
1. Velocity of three particles A, B and C varies with time t as, v A  (2 tiˆ  6 ˆj) m/s vB  (3 ˆi  4 ˆj) m/s and

vC  (6 ˆi  4 tj)
ˆ m/s. Regarding the pseudo force match the following table :–
Column I Column II
(A) On A as observed by B (p) Along positive x–direction
(B) On B as observed by C (q) Along negative x–direction
(C) On A as observed by C (r) Along positive y–direction
(D) On C as observed by A (s) Along negative y–direction
(t) Zero

2. In the diagram shown in figure (g = 10 m/s2)

Column I Column II
(A) Acceleration of 2kg block (p) 8 SI unit
(B) Net force on 3kg block (q) 25 SI unit
(C) Normal reaction between 2kg and 1kg (r) 2 SI unit
(D) Normal reaction between 3kg and 2kg (s) 45 N
(t) None

3. Match the following

Column I Column II
(A) Friction is a (P) 0 AND µkR where R is reaction force
(B) Friction force is independent of (Q) Area of surface in contact
(C) The value of static friction force lies (R) Non-conservation force
between
(D) Magnitude of static friction is (S) Kinetic friction
always greater than
(T) µsR and µkR
(U) Conservative force
(V) Rolling friction

72 etoosindia.com
India’s No. 1 Online Coaching Institute
IIT-JEE | PRE-MEDICAL | CBSE | FOUNDATION
 LAW OF MOTION & FRICTION

Exercise # 4 PART - 1 PREVIOUS YEAR (NEET/AIPMT)

1. Two masses as shown in the figure are suspended 6. 250 N force is required to raise 75 kg mass from a
from a massless pulley. The acceleration of the pulley. If rope is pulled 12 m then the load is lifted to
system when masses are left free is [2000] 3 m, the efficiency of pulley system will be [2001]
(A) 25% (B) 33.3 %
2g g
(A) (B) (C) 75% (D) 90%
3 3
7. A block of mass 10 kg placed on rough horizontal
g g
(C) (D) 5g surface having coefficient of friction  = 0.5, if a
9 7 horizontal force of 100 N acting on it then
10 g acceleration of the block will be [2002]
2. A body of mass 3 kg hits a wall at an angle of 60° (A) 10 m/s2 (B) 5 m/s2
and returns at the same angle. The impact time was (C) 15 m/s2 (D) 0.5 m/s2
0.2 sec. The force exerted on the wall [2000]
8. A lift of mass 1000 kg which is moving with
//////////////////////////

(A) 150 3 N acceleration of 1 m/s2 in upward direction, then the

60° tension developed in string which is connected to
(B) 50 3 N lift is [2002]
60° (A) 9800 N (B) 10,800 N
(C) 100 N
10 m/s (C) 11,000 N (D) 10,000 N
(D) 75 3 N
9. A monkey of mass 20 kg is holding a vertical rope.
The rope will not break when a mass of 25 kg is
3. A 1 kg stationary bomb is exploded in three parts
suspended from it but will break if the mass exceeds
having mass 1 : 1 : 3 respectively. Parts having same
25 kg. What is the maximum acceleration with which
mass move in perpendicular direction with velocity
the monkey can climb up along the rope ?
30 m/s, then the velocity of bigger part will be
(g = 10 m/s2) [2003]
10 (A) 5 m/s2 (B) 10 m/s2
(A) 10 2 m/sec (B) m/sec [2001]
2 (C) 25 m/s2 (D) 2.5 m/s2

15 10. A man weighs 80 kg. He stands on a weighing scale

(C) 15 2 m/sec (D) m/sec
2 in a lift which is moving upwards with a uniform
acceleration of 5 m/s2. What would be the reading
on the scale ? (g = 10 m/s2) [2003]
4. A cricketer catches a ball of mass 150 gm in 0.1 sec
moving with speed 20 m/s, then he experiences force (A) zero (B) 400 N
of [2001] (C) 800 N (D) 1200 N
(A) 300 N (B) 30 N
11. The coefficient of static friction, s, between block
(C) 3 N (D) 0.3 N A of mass 2 kg and the table as shown in the figure
is 0.2. What would be the two blocks do not move?
5. On the horizontal surface of a truck a block of mass The string and the pulley are assumed to be smooth
1 kg is placed ( = 0.6) and truck is moving with and massless. (g = 10 m/s2) [2004]
acceleration 5 m/sec2 then the frictional force on the (A) 2.0 kg
block will be [2001] 2 kg A
(B) 4.0 kg ////////////////////////
(A) 5 N (B) 6 N
(C) 0.2 kg
(C) 5.88 N (D) 8 N B
(D) 0.4 kg

76 etoosindia.com
Study with Best Etoos Faculties of Kota
IIT-JEE | PRE-MEDICAL | CBSE | FOUNDATION
PHYSICS FOR NEET & AIIMS

MOCK TEST
STRAIGHT OBJECTIVE TYPE
1. A light spring is compressed and placed horizontally between a vertical fixed wall
and a block free to slide over a smooth horizontal table top as shown in the figure.
The system is released from rest. The graph which represents the relation between
the magnitude of acceleration ‘ a ‘ of the block and the distance
‘ x ‘ travelled by it (as long as the spring is compressed) is:


2. In the figure shown the acceleration of A is, aA = 15î 15 ĵ then the acceleration of B is: (A remains in contact
with B)

(A) 6 î (B)  15 î (C)  10 î (D)  5 î

3. Two blocks A and B of masses m & 2m respectively are held at rest such that the spring is in natural length.
Find out the accelerations of both the blocks just after release:

g g
(A) g , g  (B)   (C) 0, 0 (D) g  0
3 3

84 etoosindia.com
India’s No. 1 Online Coaching Institute
IIT-JEE | PRE-MEDICAL | CBSE | FOUNDATION
 11th Class Modules Chapter Details

Physics Chemistry Mathematics

5 5 5
Modules Modules Modules

PHYSICS CHEMISTRY BIOLOGY

Module-1 Module-1(PC) Module-1

1. Physical World & 1. Some Basic Conceps of 1. Diversity in the Living
Measurements Chemistry World
2. Basic Maths & Vector 2. Atomic Structure 2. Plant Kingdom
3. Kinematics 3. Chemical Equilibrium 3. Animal Kingdom
4. Ionic Equilibrium
Module-2 Module-2
Module-2(PC) 1. Morphology in Flowering Plants
1. Law of Motion & Friction 1. Thermodynamics & 2. Anatomy of Flowering Plants
2. Work, Energy & Power Thermochemistry 3. Structural Organization in
2. Redox Reaction Animals
Module-3 3. States Of Matter (Gaseous &
1. Motion of system of Liquid) Module-3
particles & Rigid Body 1. Cell: The Unit of Life
2. Gravitation
Module-3(IC)
1. Periodic Table 2. Biomolecules
2. Chemical Bonding 3. Cell Cycle & Cell Division
Module-4
3. Hydrogen & Its Compounds 4. Transport in Plants
1. Mechanical Properties 4. S-Block 5. Mineral Nutrition
of Matter
2. Thermal Properties of Matter Module-4
Module-4(OC)
1. Nomenclature of 1. Photosynthesis in Higher Plants
Module-5 Organic Compounds 2. Respiration in Plants
2. Isomerism 3. Plant Growth and Development
1. Oscillations
3. General Organic Chemistry 4. Digestion & Absorption
2. Waves
5. Breathing & Exchange of Gases
Module-5(OC) Module-5
1. Reaction Mechanism
2. Hydrocarbon 1. Body Fluids & Its Circulation
3. Aromatic Hydrocarbon 2. Excretory Products & Their
4. Environmental Chemistry & Elimination
Analysis Of Organic Compounds 3. Locomotion & Its Movement
4. Neural Control & Coordination
5. Chemical Coordination and
Integration

To purchase the books, go through the link below-

http://www.etoosindia.com/smartmall/bookList.do
 12th Class Modules Chapter Details

Physics Chemistry Mathematics

5 5 5
Modules Modules Modules

PHYSICS CHEMISTRY BIOLOGY

Module-1 Module-1(PC) Module-1

1. Electrostatics 1. Solid State 1. Reproduction in Organisms
2. Capacitance 2. Chemical Kinetics 2. Sexual Reproduction in
3. Solutions and Colligative Flowering Plants
Module-2 Properties 3. Human Reproduction
4. Reproductive Health
1. Current Electricity Module-2(PC)
2. Magnetic Effect of Current
1. Electrochemistry Module-2
and Magnetism
2. Surface Chemistry 1. Principles of Inheritance and
Module-3 Variation
Module-3(IC)
2. Molecular Basis of Inheritance
1. Electromagnetic Induction 1. P-Block Elements 3. Evolution
2. Alternating Current 2. Transition Elements
(d & f block) Module-3
Module-4 3. Co-ordination Compound
4. Metallurgy 1. Human Health and Disease
1. Geometrical Optics 2. Strategies for Enhancement in
2. Wave Optics Module-4(OC) Food Production
3. Microbes in Human Welfare
Module-5 1. HaloAlkanes & HaloArenes
2. Alcohol, Phenol & Ether Module-4
1. Modern Physics 3. Aldehyde, Ketone &
2. Nuclear Physics Carboxylic Acid 1. Biotechnology: Principles and
3. Solids & Semiconductor Processes
Devices Module-5(OC) 2. Biotechnology and Its
4. Electromagnetic Waves 1. Nitrogen & Its Derivatives Applications
2. Biomolecules & Polymers 3. Organisms and Populations
3. Chemistry in Everyday Life Module-5
1. Ecosystem
2. Biodiversity and Conservation
3. Environmental Issues

To purchase the books, go through the link below-

http://www.etoosindia.com/smartmall/bookList.do