15/10/2019 T-14
LUCKNOW CENTRES
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Regd. Office : Aakash Tower, 8, Pusa Road, New Delhi-110005; Ph.: 011-47623456
Topics covered :
Physics : Work, Kinetic Energy
1. If work done by gravitational force on a body is 6. Two vehicles of masses m1 and m2 possess same
positive, then its potential energy will kinetic energy. When they are stopped by same
retarding force, then ratio of their stopping time is
(1) Decrease (2) Increase
m1 m2
(3) Constant (4) Zero (1) m (2) m
2 1
2. A body of mass 1 kg is dropped from a height
10 m. If it hits the ground with speed 10 m/s, then m2 m1
the work done by air resistance is equal to (3) m1 (4) m2
(1) –50 J (2) 50 J 7. Change in kinetic energy of a particle is equal to
(3) –100 J (4) +150 J work done on it
3. The kinetic energy K of a particle moving along a (1) For conservative force
circle of radius 2 m depends upon the distance (2) For non conservative force
covered d as K = cd 2 (c is constant). The ratio of (3) In inertial as well as non-inertial reference
tangential and centripetal acceleration at d = 2 m frame
is
(4) All of these
(1) 8 (2) 2
8. A particle of mass m is moving on a straight line
(3) 4 (4) 1 such that its velocity changes with distance
4. A particle is thrown with kinetic energy 100 J travelled as v k x . The work done by net force
straight up on a rough inclined plane of inclination on the particle during first t second is
45° and coefficient of friction is 0.2. The work done
against friction before the particle comes to rest is mk 2 t 2 mk 4 t
(1) (2)
4 8
(1) 16.6 J (2) 100 J
(3) 13 J (4) 33.3 J mk 4t 2 mk 2 t
(3) (4)
8 4
1 9. Momentum of a particle is increased by 60%. The
5. A rifle bullet loses th of its velocity in passing
N kinetic energy becomes
through a plank. The minimum number of planks
required just to stop the bullet is (1) 140% (2) 120%
(3) 256% (4) 156%
N2 N2 10. A body is moving along a straight line with force
(1) (2)
N 1 N 1 F = 2x. The work done to cover 2 m is
N2 N2 (1) 1 J (2) 2 J
(3) (4) (3) 8 J (4) 4 J
2N 1 2N 1
(1)
11. A particle of mass m is moving in a horizontal circle
3gL 3gL
k (1) (2)
of radius r with a centripetal force F 2 rˆ . The 4 8
r
total mechanical energy of the particle is gL 5gL
(3) (4)
k 3k 8 8
(1) (2)
r 2r 15. Under the action of a force a 2 kg body moves
such that its position x as a function of time is
k 3k
(3) (4) t3
2r 2r given by x , where x is in metre and t is in
3
12. By applying a f orce F (3 xy 5z ) jˆ 4zkˆ a seconds. The work done by net force in 1st two
seconds is
particle is moved along the path y = x2, where all
quantities are in SI units, from point (0, 0, 0) m to (1) 1.6 J (2) 16 J
the point (3) 160 J (4) 1600 J
(2, 4, 0) m. The work done by force F on the 16. A body of mass m is placed inside a lift as shown
particle (in joule), is in figure. Lift start accelerating with acceleration a
y in upward direction. If lift start moving from rest,
(2, 4, 0)
then the work done by normal reaction in time t is
a
Block
y = x2
Lift
x
0, 0, 0 1
(1) ma (g + a) t2 (2) Zero
2
280 140
(1) (2) 1 1
5 5 (3) m (g + a) t2 (4) mgat2
2 2
232 192 17. A block of mass m slides across a horizontal
(3) (4)
5 5
frictionless surface with speed v. It then runs into
13. A mass m is suspended by a massless string
forming a simple pendulum of length 2.0 m. The and compresses a spring system (see figure). If all
string of the pendulum is initially at an angle of 60° the springs have spring constant K, then the
with the vertically downward direction when the
distance by which the spring is compressed is
mass is released f rom rest. Centripetal
acceleration of the mass m when it is at lowest v
position, is
(g = 10 m/s )2 K
(1) 10 m/s2 (2) 5 m/s2 K
m
(3) 20 m/s2 (4) 25 m/s2 K
14. Half length of the uniform chain of length L is K
hanging and half length is placed over rough table Frictionless
having coefficient of friction = 0.5, find speed of
the chain at the moment it leaves the table mv 2 4mv 2
completely. (1) (2)
K K
= 0.5
mv 2 mv 2
(3) (4)
4K 2K
L/2
18. Two plank of masses 10 kg and 4 kg are placed 20. Kinetic energy of a particle moving on a straight
on a horizontal plane as shown in figure. There is line is given by K = t2, where is some positive
no friction between plane and 10 kg block and constant. The force acting on the particle is (if
= 0.8 between 10 kg and 4 kg. A horizontal force particle starts from rest)
of 70 N is applied on 10 kg block. The work done (1) Constant
by frictional force on the block in first two second is
(2) Decreasing
= 0.8 4 kg (3) Increasing
10 kg 70 N =0 (4) First increases then decreases
21. In following arrangement all surfaces are smooth
(1) 200 J (2) Zero and pulleys are light. The system is released from
rest.
(3) – 200 J (4) 400 J
19. Velocity-time graph of a particle moving in a straight m = 3 kg m = 3 kg
line is shown in figure. Mass of particle is 4 kg. B C
Work done by all the forces acting on the particle
between time interval t = 0 to t = 4 s is
v (m/s) A m = 3 kg
20 m/s
The work done by tension on block B till the block
6
0 t (s) A falls through height 1 m
4
– 20 m/s (1) 5 J
(2) 7 J
(3) 10 J
(1) 40 J (2) 20 J
(4) 7.5 J
(3) Zero (4) 10 J
