Laws Of Motion CBSE Questions & Answers

Laws Of Motion

This is Physics Class 11 Laws of Motion CBSE Questions & Answers. There are 15 questions in this test with each question having around four answer choices.

Questions & Answers

Neglecting air resistance, in which of the following cases the net force acting on a stone of mass 0.1 kg non zero?

A
just after it is dropped from the window of a stationary train
B
lying on the floor of a train which is accelerating with 1 m \({{\rm{s}}^{ - {\rm{2}}}}\) , the stone being at rest relative to the train
Correct
C
just after it is dropped from the window of a train accelerating with 1 m \({{\rm{s}}^{ - {\rm{2}}}}\)
D
just after it is dropped from the window of a train running at a constant velocity of 36 km/h

Give the magnitude and direction of the net force acting on a stone of mass 0.1 kg lying on the floor of a train which is accelerating with 1 m \({{\rm{s}}^{ - {\rm{2}}}}\), the stone being at rest relative to the train. Neglect air resistance.

A
0.2 opposite to the direction of motion
B
1.0 N in the direction of motion
C
0.1 N opposite to the direction of motion
D
0.1 N in the direction of motion
Correct

One end of a string of length l is connected to a particle of mass m and the other to a small peg on a smooth horizontal table. If the particle moves in a circle with speed v, T is the tension in the string, the net force on the particle directed towards the centre is

A
\({\rm{T}} - {{{\rm{m}}{{\rm{v}}^2}} \over {\rm{l}}}\)
B
\({\rm{T}} + {{{\rm{m}}{{\rm{v}}^2}} \over {\rm{l}}}\)
C
T
Correct
D
0

A constant retarding force of 50 N is applied to a body of mass 20 kg moving initially with a speed of 15 m \({{\rm{s}}^{ - {\rm{1}}}}\). How long does the body take to stop?

A
6.0 s
Correct
B
7.0 s
C
4.0 s
D
5.0 s

A constant force acting on a body of mass 3.0 kg changes its speed from 2.0 m \({{\rm{s}}^{ - {\rm{1}}}}\) to 3.5 m \({{\rm{s}}^{ - {\rm{1}}}}\) in 25 s. The direction of the motion of the body remains unchanged. What is the magnitude and direction of the force?

A
0.09 m \({{\rm{s}}^{ - {\rm{2}}}}\), 0.12 N in the direction of motion
B
0.06 m \({{\rm{s}}^{ - {\rm{2}}}}\), 0.18 N in the direction of motion
Correct
C
0.08 m \({{\rm{s}}^{ - {\rm{2}}}}\), 0.14 N in the direction of motion
D
0.07 m \({{\rm{s}}^{ - {\rm{2}}}}\), 0.16 N in the direction of motion

A body of mass 5 kg is acted upon by two perpendicular forces 8 N and 6 N. Give the magnitude and direction of the acceleration of the body.

A
16 N at an angle of 46\(^\circ \) to the 8 N force
B
14 N at an angle of 37\(^\circ \) to the 8 N force
C
10 N at an angle of 36\(^\circ \) to the 8 N force
Correct
D
12 N at an angle of 38\(^\circ \) to the 8 N force

The driver of a three-wheeler moving with a speed of 36 km/h sees a child standing in the middle of the road and brings his vehicle to rest in 4.0 s just in time to save the child. What is the average retarding force on the vehicle? The mass of the three-wheeler is 400 kg and the mass of the driver is 65 kg.

A
– 2.2 m \({{\rm{s}}^{ - {\rm{2}}}}\), 900 N
B
– 2.3 m \({{\rm{s}}^{ - {\rm{2}}}}\), 1000 N
C
– 2.5 m\({{\rm{s}}^{ - {\rm{2}}}}\) , 1200 N
Correct
D
– 2.4 m \({{\rm{s}}^{ - {\rm{2}}}}\), 1100 N

A rocket with a lift-off mass 20,000 kg is blasted upwards with an initial acceleration of 5.0 m s-2. Calculate the initial thrust (force) of the blast.

A
300000 N
Correct
B
350000 N
C
365000 N
D
378000 N

A body of mass 0.40 kg moving initially with a constant speed of 10 m \({{\rm{s}}^{ - {\rm{2}}}}\) to the north is subject to a constant force of 8.0 N directed towards the south for 30 s. Take the instant the force is applied to be t = 0, the position of the body at that time to be x = 0, and predict its position at t = –5 s.

A
-50 m
Correct
B
50 m
C
-55 m
D
-60 m

A body of mass 0.40 kg moving initially with a constant speed of 10 m \({{\rm{s}}^{ - {\rm{1}}}}\) to the north is subject to a constant force of 8.0 N directed towards the south for 30 s. Take the instant the force is applied to be t = 0, the position of the body at that time to be x = 0, and predict its position at t = –25 s.

A
-8.0 km
B
-7 km
C
-6 km
Correct
D
-7.5 km

A body of mass 0.40 kg moving initially with a constant speed of 10 m \({{\text{s}}^{ - {\text{1}}}}\) to the north is subject to a constant force of 8.0 N directed towards the south for 30 s. Take the instant the force is applied to be t = 0, the position of the body at that time to be x = 0, and predict its position at t = –100 s

A
-50 km
Correct
B
-55 km
C
-60 km
D
-67 km

A truck starts from rest and accelerates uniformly at 2.0 m \({{\rm{s}}^{ - {\rm{2}}}}\). At t = 10 s, a stone is dropped by a person standing on the top of the truck (6 m high from the ground). What is the magnitude of velocity (in m \({{\rm{s}}^{ - {\rm{1}}}}\) ) of the stone at t = 11s? (Neglect air resistance.)

A
19.6
B
18.5
C
22.4
Correct
D
21.0

A truck starts from rest and accelerates uniformly at 2.0 m \({{\rm{s}}^{ - {\rm{2}}}}\). At t = 10 s, a stone is dropped by a person standing on the top of the truck (6 m high from the ground). What is the magnitude of acceleration (in m \({{\rm{s}}^{ - {\rm{2}}}}\) ) of the stone at t = 11s? (Neglect air resistance.)

A
10.0
Correct
B
8
C
14
D
12

A bob of mass 0.1 kg hung from the ceiling of a room by a string 2 m long is set into oscillation. The speed of the bob at its mean position is 1 m \({{\rm{s}}^{ - {\rm{1}}}}\).What is the trajectory of the bob if the string is cut when the bob is at one of its extreme positions

A
bob will go upwards
B
bob will fall vertically downwards
Correct
C
bob will go downwards at an angle
D
bob will go down in a parabolic path

A
bob will fall vertically downwards
B
bob will fall vertically downwards
C
bob will go down in a parabolic path
Correct
D
bob will go upwards