Laws of Motion- 1 Practice Questions - DPP for NEET

 Page 1


DIRECTIONS (Q.1-Q.20) : There are 20 multiple choice
questions. Each question has 4 choices (a), (b), (c) and (d), out
of which ONLY ONE choice is correct.
Q.1 A boy standing on a weighing machine observes his weight
as 200 N. When he suddenly jumpes upwards, his friend
notices that the reading increased to 400 N. The
acceleration by which the boy jumped will be-
(a) 9.8 m/s
2
(b) 29.4 m/s
2
(c) 4.9 m/s
2
(d) 14.7 m/s
2
Q.2 A force of (6
i
ˆ
+ 8 j
ˆ
) N acted on a body of mass 10 kg. The
displacement after 10 sec, if it starts from rest, will be -
(a) 50 m along tan
–1
 4/3 with x axis
(b) 70 m along tan
–1
 3/4 with x axis
(c) 10 m along tan
–1
 4/3 with x axis
(d) None
Q.3 A boat of mass 1000 kg is moving with a velocity of
5 m/s. A person of mass 60 kg jumps into the boat. The
velocity of the boat with the person will be -
(a) 4.71 m/s (b) 4.71 cm/s
(c) 47.1 m/s (d) 47.1 cm/s
Q.4 A disc of mass 10 gm is kept horizontally in air by firing
bullets of mass 5 g each at the rate of 10/s. If the bullets
rebound with same speed. The velocity with which the
bullets are fired is -
(a) 49 cm/s (b) 98 cm/s (c)  147 cm/s (d) 196 cm/s
Q.5 A fire man has to carry an injured person of mass 40 kg
from the top of a building with the help of the rope which
can withstand a load of 100 kg. The acceleration of the
fireman if his mass is 80 kg, will be-
(a) 8.17 m/s
2
(b) 9.8 m/s
2
(c) 1.63 m/s
2
(d) 17.97 m/s
2
Page 2


DIRECTIONS (Q.1-Q.20) : There are 20 multiple choice
questions. Each question has 4 choices (a), (b), (c) and (d), out
of which ONLY ONE choice is correct.
Q.1 A boy standing on a weighing machine observes his weight
as 200 N. When he suddenly jumpes upwards, his friend
notices that the reading increased to 400 N. The
acceleration by which the boy jumped will be-
(a) 9.8 m/s
2
(b) 29.4 m/s
2
(c) 4.9 m/s
2
(d) 14.7 m/s
2
Q.2 A force of (6
i
ˆ
+ 8 j
ˆ
) N acted on a body of mass 10 kg. The
displacement after 10 sec, if it starts from rest, will be -
(a) 50 m along tan
–1
 4/3 with x axis
(b) 70 m along tan
–1
 3/4 with x axis
(c) 10 m along tan
–1
 4/3 with x axis
(d) None
Q.3 A boat of mass 1000 kg is moving with a velocity of
5 m/s. A person of mass 60 kg jumps into the boat. The
velocity of the boat with the person will be -
(a) 4.71 m/s (b) 4.71 cm/s
(c) 47.1 m/s (d) 47.1 cm/s
Q.4 A disc of mass 10 gm is kept horizontally in air by firing
bullets of mass 5 g each at the rate of 10/s. If the bullets
rebound with same speed. The velocity with which the
bullets are fired is -
(a) 49 cm/s (b) 98 cm/s (c)  147 cm/s (d) 196 cm/s
Q.5 A fire man has to carry an injured person of mass 40 kg
from the top of a building with the help of the rope which
can withstand a load of 100 kg. The acceleration of the
fireman if his mass is 80 kg, will be-
(a) 8.17 m/s
2
(b) 9.8 m/s
2
(c) 1.63 m/s
2
(d) 17.97 m/s
2
2
DPP/ P 09
Q.6 A body of mass 0.02 kg falls from a height of 5 metre into
a pile of sand. The body penetrates the sand a distance of 5
cm before stoping. What force has the sand exerted on the
body ?
(a) 1.96 N (b) –19.6 N
(c) –0.196 N (d) 0.0196 N
Q.7 The magnitude of the force (in newton) acting on a body
varies with time t (in microsecond) as shown in fig. AB,
BC, and CD are straight line segments. The magnitude of
the total impulse of the force on the body from t = 4 ms to
t = 16 ms is
(a) 5 × 10
–4
 N.s
(b) 5 × 10
–3
 N.s
C
D
0
A B
F E
Force F (N)
800
600
400
200
2 4 6 8 10 12 1416
Time ( s)
____
m
(c) 5 × 10
–5
 N.s
(d) 5 × 10
–2
 N.s
Q.8 The total mass of an elevator with a 80 kg man in it is 1000
kg. This elevator moving upward with a speed of 8 m/sec,
is brought to rest over a distance of 16m. The tension T in
the cables supporting the elevator and the force exerted
on the man by the elevator floor will respectively be-
(a) 7800 N, 624 N (b) 624 N, 7800 N
(c) 78 N, 624 N (d) 624 N, 78 N
Q.9 In the arrangement shown in fig. the ends P and Q of an
unstretchable string move downwards with a uniform speed
U. Pulleys A and B are fixed. Mass M moves upwards with
a speed of
A
B
Q
M
q
q
P
(a) 2U cos q (b) U cos q
(c) 2U/cos q (d) U/cos q
Q.10 An engine of mass 5 × 10
4
 kg pulls a coach of mass 4 ×
10
4
 kg. Suppose that there is a resistance of 1 N per 100
kg acting on both coach and engine, and that the driving
force of engine is 4500 N. The acceleration of the engine
and tension in the coupling will respectively be-
(a) 0.04 m/s
2
, 2000 N (b) 0.4 m/s
2
, 200 N
(c) 0.4 m/s
2
, 20 N (d) 4 m/s
2
, 200 N
Q.11 A body whose mass 6 kg is acted upon by two forces
ˆˆ
(8i 10j) + N and 
ˆˆ
(4i 8j) + N. The acceleration produced will
be (in m/s
2
) –
(a)
ˆˆ
(3i 2j) + (b)
ˆˆ
12i 18j +
(c)
1
ˆˆ
(i j)
3
+ (d)
ˆˆ
2i 3j +
Q.12 A car of 1000 kg moving with a velocity of  18 km/hr is
stopped by the brake force of 1000 N. The distance covered
by it before coming to rest is -
(a) 1 m (b) 162 m (c) 12.5 m (d) 144 m
Q.13 A block of metal weighing 2 kg is resting on a frictionless
plane. It is struck by a jet releasing water at a rate of 1 kg/
s and at a speed of 5 m/s. The initial acceleration of the
block will be –
(a) 2.5 m/s
2
(b) 5 m/s
2
(c) 0.4 m/s
2
(d)0
Q.14 A man fires the bullets of mass  m each with the velocity v
with the help of machine gun, if he fires n bullets every
sec, the reaction force per second on the man will be -
(a)
m
v
n (b) m n v (c)
mv
n
(d)
vn
m
Q.15 A body of mass 15 kg moving with a velocity of 10 m/s is
to be stopped by a resistive force in 15 sec, the force will
be -
(a) 10 N (b) 5 N
(c) 100 N (d) 50 N
Q.16 A cricket ball of mass 250 gm moving with a velocity of
24 m/s is hit by a bat so that it acquires a velocity of 28 m/
s in the opposite direction. The force acting on the ball, if
the contact time is 1/100 of a second, will be -
(a) 1300 N in the final direction of ball
(b) 13 N in the initial direction of ball
(c) 130 N in the final direction of ball
(d) 1.3 N in the initial direction of ball
Page 3


DIRECTIONS (Q.1-Q.20) : There are 20 multiple choice
questions. Each question has 4 choices (a), (b), (c) and (d), out
of which ONLY ONE choice is correct.
Q.1 A boy standing on a weighing machine observes his weight
as 200 N. When he suddenly jumpes upwards, his friend
notices that the reading increased to 400 N. The
acceleration by which the boy jumped will be-
(a) 9.8 m/s
2
(b) 29.4 m/s
2
(c) 4.9 m/s
2
(d) 14.7 m/s
2
Q.2 A force of (6
i
ˆ
+ 8 j
ˆ
) N acted on a body of mass 10 kg. The
displacement after 10 sec, if it starts from rest, will be -
(a) 50 m along tan
–1
 4/3 with x axis
(b) 70 m along tan
–1
 3/4 with x axis
(c) 10 m along tan
–1
 4/3 with x axis
(d) None
Q.3 A boat of mass 1000 kg is moving with a velocity of
5 m/s. A person of mass 60 kg jumps into the boat. The
velocity of the boat with the person will be -
(a) 4.71 m/s (b) 4.71 cm/s
(c) 47.1 m/s (d) 47.1 cm/s
Q.4 A disc of mass 10 gm is kept horizontally in air by firing
bullets of mass 5 g each at the rate of 10/s. If the bullets
rebound with same speed. The velocity with which the
bullets are fired is -
(a) 49 cm/s (b) 98 cm/s (c)  147 cm/s (d) 196 cm/s
Q.5 A fire man has to carry an injured person of mass 40 kg
from the top of a building with the help of the rope which
can withstand a load of 100 kg. The acceleration of the
fireman if his mass is 80 kg, will be-
(a) 8.17 m/s
2
(b) 9.8 m/s
2
(c) 1.63 m/s
2
(d) 17.97 m/s
2
2
DPP/ P 09
Q.6 A body of mass 0.02 kg falls from a height of 5 metre into
a pile of sand. The body penetrates the sand a distance of 5
cm before stoping. What force has the sand exerted on the
body ?
(a) 1.96 N (b) –19.6 N
(c) –0.196 N (d) 0.0196 N
Q.7 The magnitude of the force (in newton) acting on a body
varies with time t (in microsecond) as shown in fig. AB,
BC, and CD are straight line segments. The magnitude of
the total impulse of the force on the body from t = 4 ms to
t = 16 ms is
(a) 5 × 10
–4
 N.s
(b) 5 × 10
–3
 N.s
C
D
0
A B
F E
Force F (N)
800
600
400
200
2 4 6 8 10 12 1416
Time ( s)
____
m
(c) 5 × 10
–5
 N.s
(d) 5 × 10
–2
 N.s
Q.8 The total mass of an elevator with a 80 kg man in it is 1000
kg. This elevator moving upward with a speed of 8 m/sec,
is brought to rest over a distance of 16m. The tension T in
the cables supporting the elevator and the force exerted
on the man by the elevator floor will respectively be-
(a) 7800 N, 624 N (b) 624 N, 7800 N
(c) 78 N, 624 N (d) 624 N, 78 N
Q.9 In the arrangement shown in fig. the ends P and Q of an
unstretchable string move downwards with a uniform speed
U. Pulleys A and B are fixed. Mass M moves upwards with
a speed of
A
B
Q
M
q
q
P
(a) 2U cos q (b) U cos q
(c) 2U/cos q (d) U/cos q
Q.10 An engine of mass 5 × 10
4
 kg pulls a coach of mass 4 ×
10
4
 kg. Suppose that there is a resistance of 1 N per 100
kg acting on both coach and engine, and that the driving
force of engine is 4500 N. The acceleration of the engine
and tension in the coupling will respectively be-
(a) 0.04 m/s
2
, 2000 N (b) 0.4 m/s
2
, 200 N
(c) 0.4 m/s
2
, 20 N (d) 4 m/s
2
, 200 N
Q.11 A body whose mass 6 kg is acted upon by two forces
ˆˆ
(8i 10j) + N and 
ˆˆ
(4i 8j) + N. The acceleration produced will
be (in m/s
2
) –
(a)
ˆˆ
(3i 2j) + (b)
ˆˆ
12i 18j +
(c)
1
ˆˆ
(i j)
3
+ (d)
ˆˆ
2i 3j +
Q.12 A car of 1000 kg moving with a velocity of  18 km/hr is
stopped by the brake force of 1000 N. The distance covered
by it before coming to rest is -
(a) 1 m (b) 162 m (c) 12.5 m (d) 144 m
Q.13 A block of metal weighing 2 kg is resting on a frictionless
plane. It is struck by a jet releasing water at a rate of 1 kg/
s and at a speed of 5 m/s. The initial acceleration of the
block will be –
(a) 2.5 m/s
2
(b) 5 m/s
2
(c) 0.4 m/s
2
(d)0
Q.14 A man fires the bullets of mass  m each with the velocity v
with the help of machine gun, if he fires n bullets every
sec, the reaction force per second on the man will be -
(a)
m
v
n (b) m n v (c)
mv
n
(d)
vn
m
Q.15 A body of mass 15 kg moving with a velocity of 10 m/s is
to be stopped by a resistive force in 15 sec, the force will
be -
(a) 10 N (b) 5 N
(c) 100 N (d) 50 N
Q.16 A cricket ball of mass 250 gm moving with a velocity of
24 m/s is hit by a bat so that it acquires a velocity of 28 m/
s in the opposite direction. The force acting on the ball, if
the contact time is 1/100 of a second, will be -
(a) 1300 N in the final direction of ball
(b) 13 N in the initial direction of ball
(c) 130 N in the final direction of ball
(d) 1.3 N in the initial direction of ball
DPP/ P 09
3
Q.17 A force of 2 N is applied on a particle for 2 sec, the change
in momentum will be -
(a) 2 Ns (b) 4 Ns (c) 6 Ns (d) 3 Ns
Q.18A body of mass 2 kg is moving along x-direction with a
velocity of 2 m/sec. If a force of 4 N is applied on it along
y-direction for 1 sec, the final velocity  of particle will be -
(a) 22 m/s (b) 2 m/s
(c) 1/2 m/s (d) 1/22 m/s
Q.19 A cricket ball of mass 150 g is moving with a velocity of
12m/sec and is hit by a bat so that the ball is turned back
with a velocity of 20 m/sec, the  force on the ball acts for
0.01 sec, then the average force exerted by the bat on the
ball will be
(a) 48 N (b) 40 N (c) 480 N (d) 400 N
Q.20A body of mass 20 kg moving with a velocity of 3 m/s,
rebounds on a wall with same velocity . The impulse on the
body is -
(a) 60 Ns (b) 120 Ns (c) 30 Ns (d) 180 Ns
DIRECTIONS (Q.21-Q.23) : In the following questions,
more than one of the answers  given are correct. Select the
correct answers and mark it according to the following
codes:
Codes :
(a) 1, 2 and 3 are correct (b) 1 and 2 are correct
(c) 2 and 4 are correct (d) 1 and 3 are correct
Q.21 A mass of 60 kg is on the floor of a lift moving down. The
lift moves at first with an acceleration of  3 m/sec
2
, then
with constant velocity and finally with a retardation of
3m/sec
2
. Choose the correct options related to possible
reactions exerted by the lift on the body in each part of the
motion –
(1) 408 N (2) 588 N (3) 768 N (4) 508 N
Q.22 A mass of 10 kg is hung to a spring balance in lift. If the
lift is moving with an acceleration g/3 in upward &
downward directions, choose the correct options related
to the reading of the spring balance.
(1) 13.3 kg (2) 6.67 kg (3) 32.6 kg (4) 0
Q.23Choose the correct options
(1) A reference frame in which Newton’s first law is valid
is called an inertial reference frame.
(2) Frame moving at constant velocity relative to a known
inertial frame is also an inertial frame.
(3) Idealy, no inertial frame exists in the universe for
practical purpose, a frame of reference may be
considered as inertial if its acceleration is negligible
with respect to the acceleration of the object to be
observed.
(4) To measure the acceleration of a falling apple, earth
cannot be considered as an inertial frame.
DIRECTIONS (Q.24-Q.26) : Read the passage given below
and answer the questions that follows :
Pseudo force is an imaginary force which is recognised only by a
non-inertial observer to explain the physical situation according
to newton’s laws. Magnitude of pseudo force F
p
 is equal to the
product of the mass m of the object and the acceleration a of the
frame of reference.  The direction of the force is opposite to the
direction of acceleration,  F
p
 = –ma
Q.24A spring weighing machine inside a stationary lift reads
50 kg when a man stand on it. What would happen to the
scale reading if the lift is moving upward with (i) constant
velocity (ii) constant acceleratioin ?
(a) 50 kg wt, 
50a
50
g
æö
+
ç÷
èø
kg wt
(b) 50 kg wt, 
50g
50
a
æö
+
ç÷
èø
 kg wt
(c) 50 kg wt, 
50a
g
æö
ç÷
èø
 kg wt
(d) 50 kg wt, 
50g
a
æö
ç÷
èø
 kg wt
Q.25A 25 kg lift is supported by a cable. The acceleration of
the lift when the tension in the cable is 175 N, will be -
(a) 2.8 m/s
2
(b) 16.8 m/s
2
(c) – 9.8 m/s
2
(d) 14 m/s
2
Page 4


DIRECTIONS (Q.1-Q.20) : There are 20 multiple choice
questions. Each question has 4 choices (a), (b), (c) and (d), out
of which ONLY ONE choice is correct.
Q.1 A boy standing on a weighing machine observes his weight
as 200 N. When he suddenly jumpes upwards, his friend
notices that the reading increased to 400 N. The
acceleration by which the boy jumped will be-
(a) 9.8 m/s
2
(b) 29.4 m/s
2
(c) 4.9 m/s
2
(d) 14.7 m/s
2
Q.2 A force of (6
i
ˆ
+ 8 j
ˆ
) N acted on a body of mass 10 kg. The
displacement after 10 sec, if it starts from rest, will be -
(a) 50 m along tan
–1
 4/3 with x axis
(b) 70 m along tan
–1
 3/4 with x axis
(c) 10 m along tan
–1
 4/3 with x axis
(d) None
Q.3 A boat of mass 1000 kg is moving with a velocity of
5 m/s. A person of mass 60 kg jumps into the boat. The
velocity of the boat with the person will be -
(a) 4.71 m/s (b) 4.71 cm/s
(c) 47.1 m/s (d) 47.1 cm/s
Q.4 A disc of mass 10 gm is kept horizontally in air by firing
bullets of mass 5 g each at the rate of 10/s. If the bullets
rebound with same speed. The velocity with which the
bullets are fired is -
(a) 49 cm/s (b) 98 cm/s (c)  147 cm/s (d) 196 cm/s
Q.5 A fire man has to carry an injured person of mass 40 kg
from the top of a building with the help of the rope which
can withstand a load of 100 kg. The acceleration of the
fireman if his mass is 80 kg, will be-
(a) 8.17 m/s
2
(b) 9.8 m/s
2
(c) 1.63 m/s
2
(d) 17.97 m/s
2
2
DPP/ P 09
Q.6 A body of mass 0.02 kg falls from a height of 5 metre into
a pile of sand. The body penetrates the sand a distance of 5
cm before stoping. What force has the sand exerted on the
body ?
(a) 1.96 N (b) –19.6 N
(c) –0.196 N (d) 0.0196 N
Q.7 The magnitude of the force (in newton) acting on a body
varies with time t (in microsecond) as shown in fig. AB,
BC, and CD are straight line segments. The magnitude of
the total impulse of the force on the body from t = 4 ms to
t = 16 ms is
(a) 5 × 10
–4
 N.s
(b) 5 × 10
–3
 N.s
C
D
0
A B
F E
Force F (N)
800
600
400
200
2 4 6 8 10 12 1416
Time ( s)
____
m
(c) 5 × 10
–5
 N.s
(d) 5 × 10
–2
 N.s
Q.8 The total mass of an elevator with a 80 kg man in it is 1000
kg. This elevator moving upward with a speed of 8 m/sec,
is brought to rest over a distance of 16m. The tension T in
the cables supporting the elevator and the force exerted
on the man by the elevator floor will respectively be-
(a) 7800 N, 624 N (b) 624 N, 7800 N
(c) 78 N, 624 N (d) 624 N, 78 N
Q.9 In the arrangement shown in fig. the ends P and Q of an
unstretchable string move downwards with a uniform speed
U. Pulleys A and B are fixed. Mass M moves upwards with
a speed of
A
B
Q
M
q
q
P
(a) 2U cos q (b) U cos q
(c) 2U/cos q (d) U/cos q
Q.10 An engine of mass 5 × 10
4
 kg pulls a coach of mass 4 ×
10
4
 kg. Suppose that there is a resistance of 1 N per 100
kg acting on both coach and engine, and that the driving
force of engine is 4500 N. The acceleration of the engine
and tension in the coupling will respectively be-
(a) 0.04 m/s
2
, 2000 N (b) 0.4 m/s
2
, 200 N
(c) 0.4 m/s
2
, 20 N (d) 4 m/s
2
, 200 N
Q.11 A body whose mass 6 kg is acted upon by two forces
ˆˆ
(8i 10j) + N and 
ˆˆ
(4i 8j) + N. The acceleration produced will
be (in m/s
2
) –
(a)
ˆˆ
(3i 2j) + (b)
ˆˆ
12i 18j +
(c)
1
ˆˆ
(i j)
3
+ (d)
ˆˆ
2i 3j +
Q.12 A car of 1000 kg moving with a velocity of  18 km/hr is
stopped by the brake force of 1000 N. The distance covered
by it before coming to rest is -
(a) 1 m (b) 162 m (c) 12.5 m (d) 144 m
Q.13 A block of metal weighing 2 kg is resting on a frictionless
plane. It is struck by a jet releasing water at a rate of 1 kg/
s and at a speed of 5 m/s. The initial acceleration of the
block will be –
(a) 2.5 m/s
2
(b) 5 m/s
2
(c) 0.4 m/s
2
(d)0
Q.14 A man fires the bullets of mass  m each with the velocity v
with the help of machine gun, if he fires n bullets every
sec, the reaction force per second on the man will be -
(a)
m
v
n (b) m n v (c)
mv
n
(d)
vn
m
Q.15 A body of mass 15 kg moving with a velocity of 10 m/s is
to be stopped by a resistive force in 15 sec, the force will
be -
(a) 10 N (b) 5 N
(c) 100 N (d) 50 N
Q.16 A cricket ball of mass 250 gm moving with a velocity of
24 m/s is hit by a bat so that it acquires a velocity of 28 m/
s in the opposite direction. The force acting on the ball, if
the contact time is 1/100 of a second, will be -
(a) 1300 N in the final direction of ball
(b) 13 N in the initial direction of ball
(c) 130 N in the final direction of ball
(d) 1.3 N in the initial direction of ball
DPP/ P 09
3
Q.17 A force of 2 N is applied on a particle for 2 sec, the change
in momentum will be -
(a) 2 Ns (b) 4 Ns (c) 6 Ns (d) 3 Ns
Q.18A body of mass 2 kg is moving along x-direction with a
velocity of 2 m/sec. If a force of 4 N is applied on it along
y-direction for 1 sec, the final velocity  of particle will be -
(a) 22 m/s (b) 2 m/s
(c) 1/2 m/s (d) 1/22 m/s
Q.19 A cricket ball of mass 150 g is moving with a velocity of
12m/sec and is hit by a bat so that the ball is turned back
with a velocity of 20 m/sec, the  force on the ball acts for
0.01 sec, then the average force exerted by the bat on the
ball will be
(a) 48 N (b) 40 N (c) 480 N (d) 400 N
Q.20A body of mass 20 kg moving with a velocity of 3 m/s,
rebounds on a wall with same velocity . The impulse on the
body is -
(a) 60 Ns (b) 120 Ns (c) 30 Ns (d) 180 Ns
DIRECTIONS (Q.21-Q.23) : In the following questions,
more than one of the answers  given are correct. Select the
correct answers and mark it according to the following
codes:
Codes :
(a) 1, 2 and 3 are correct (b) 1 and 2 are correct
(c) 2 and 4 are correct (d) 1 and 3 are correct
Q.21 A mass of 60 kg is on the floor of a lift moving down. The
lift moves at first with an acceleration of  3 m/sec
2
, then
with constant velocity and finally with a retardation of
3m/sec
2
. Choose the correct options related to possible
reactions exerted by the lift on the body in each part of the
motion –
(1) 408 N (2) 588 N (3) 768 N (4) 508 N
Q.22 A mass of 10 kg is hung to a spring balance in lift. If the
lift is moving with an acceleration g/3 in upward &
downward directions, choose the correct options related
to the reading of the spring balance.
(1) 13.3 kg (2) 6.67 kg (3) 32.6 kg (4) 0
Q.23Choose the correct options
(1) A reference frame in which Newton’s first law is valid
is called an inertial reference frame.
(2) Frame moving at constant velocity relative to a known
inertial frame is also an inertial frame.
(3) Idealy, no inertial frame exists in the universe for
practical purpose, a frame of reference may be
considered as inertial if its acceleration is negligible
with respect to the acceleration of the object to be
observed.
(4) To measure the acceleration of a falling apple, earth
cannot be considered as an inertial frame.
DIRECTIONS (Q.24-Q.26) : Read the passage given below
and answer the questions that follows :
Pseudo force is an imaginary force which is recognised only by a
non-inertial observer to explain the physical situation according
to newton’s laws. Magnitude of pseudo force F
p
 is equal to the
product of the mass m of the object and the acceleration a of the
frame of reference.  The direction of the force is opposite to the
direction of acceleration,  F
p
 = –ma
Q.24A spring weighing machine inside a stationary lift reads
50 kg when a man stand on it. What would happen to the
scale reading if the lift is moving upward with (i) constant
velocity (ii) constant acceleratioin ?
(a) 50 kg wt, 
50a
50
g
æö
+
ç÷
èø
kg wt
(b) 50 kg wt, 
50g
50
a
æö
+
ç÷
èø
 kg wt
(c) 50 kg wt, 
50a
g
æö
ç÷
èø
 kg wt
(d) 50 kg wt, 
50g
a
æö
ç÷
èø
 kg wt
Q.25A 25 kg lift is supported by a cable. The acceleration of
the lift when the tension in the cable is 175 N, will be -
(a) 2.8 m/s
2
(b) 16.8 m/s
2
(c) – 9.8 m/s
2
(d) 14 m/s
2
4
DPP/ P 09
Q.26 A body is suspended by a string from the ceiling of an
elevator. It is observed that the tension in the string is
doubled when the elevator is accelerated. The acceleration
will be -
(a) 4.9 m/s
2
(b) 9.8 m/s
2
(c) 19.6 m/s
2
(d) 2.45 m/s
2
DIRECTIONS (Q. 27-Q.29) : Each of these questions contains
two statements: Statement-1 (Assertion) and Statement-2
(Reason). Each of these questions has four alternative choices,
only one of which is the correct answer. You have to select the
correct choice.
(a) Statement-1 is True, Statement-2 is True; Statement-2 is a
correct explanation for  Statement-1.
(b) Statement-1 is True, Statement-2 is True; Statement-2 is NOT
a correct explanation for Statement-1.
(c) Statement-1 is False, Statement-2 is True.
(d) Statement-1 is True, Statement-2 is False.
Q.27 Statement-1 : A cloth covers a table. Some dishes are kept
on it. The cloth can be pulled out without dislodging the
dishes from the table.
Statement-2 : To every action there is an equal and oppo-
site reaction.
Q.28 Statement-1 : If the net external force on the body is zero
then its acceleration is zero.
Statement-2 : Acceleration does not depend on force.
Q.29 Statement-1 : The slope of momentum versus time graph
give us the acceleration.
Statement-2 : Force is given by the rate of change of
momentum.