CBSE Class 11 Physics Laws of Motion Worksheet Set A

Question. Physical independence of force is a consequence of
(a) third law of motion
(b) second law of motion
(c) first law of motion
(d) all of these laws
Answer. C

Question. A stone is dropped from a height h. It hits the ground with a certain momentum P. If the same stone is dropped from a height 100% more than the previous height, the momentum when it hits the ground will change by
(a) 68%
(b) 41%
(c) 200%
(d) 100% 
Answer. B

Question. A cricketer catches a ball of mass 150 gm in 0.1 sec moving with speed 20 m/s, then he experiences force of
(a) 300 N
(b) 30 N
(c) 3 N
(d) 0.3 N
Answer. B

Question. If the force on a rocket, moving with a velocity of 300 m/s is 210 N, then the rate of combustion of the fuel is
(a) 0.07 kg/s
(b) 1.4 kg/s
(c) 0.7 kg/s
(d) 10.7 kg/s 
Answer. C

Question. A bullet is fired from a gun. The force on the bullet is given by F = 600 – 2 × 10⁵ t where, F is in newton and t in seconds. The force on the bullet becomes zero as soon as it leaves the barrel. What is the average impulse imparted to the bullet?
(a) 9 Ns
(b) zero
(c) 1.8 Ns
(d) 0.9 Ns 
Answer. D

Question. A 5000 kg rocket is set for vertical firing. The exhaust speed is 800 m s^–1. To give an initial upward acceleration of 20 m s–2, the amount of gas ejected per second to supply the needed thrust will be (g = 10 m s^–2)
(a) 185.5 kg s^–1
(b) 187.5 kg s^–1
(c) 127.5 kg s^–1
(d) 137.5 kg s^–1
Answer. B

Question. A force of 6 N acts on a body at rest and of mass 1 kg. During this time, the body attains a velocity of 30 m/s. The time for which the force acts on the body is
(a) 7 seconds
(b) 5 seconds
(c) 10 seconds
(d) 8 seconds
Answer. B

Question. A 10 N force is applied on a body produce in it an acceleration of 1 m/s². The mass of the body is
(a) 15 kg
(b) 20 kg
(c) 10 kg
(d) 5 kg
Answer. C

Question. In a rocket, fuel burns at the rate of 1 kg/s. This fuel is ejected from the rocket with a velocity of 60 km/s.This exerts a force on the rocket equal to
(a) 6000 N
(b) 60000 N
(c) 60 N
(d) 600 N
Answer. B

Question. A 600 kg rocket is set for a vertical firing. If the exhaust speed is 1000 m s^–1, the mass of the gas ejected per second to supply the thrust needed to overcome the weight of rocket is
(a) 117.6 kg s^–1
(b) 58.6 kg s^–1
(c) 6 kg s^–1
(d) 76.4 kg s^–1
Answer. C

Question. A body of mass M hits normally a rigid wall with velocity V and bounces back with the same velocity.The impulse experienced by the body is
(a) MV
(b) 1.5MV
(c) 2MV
(d) zero
Answer. C

Question. A 0.5 kg ball moving with a speed of 12 m/s strikes a hard wall at an angle of 30° with the wall. It is reflected with the same speed at the same angle. If the ball is in contact with the wall for 0.25 seconds, the average force acting on the wall is
(a) 96 N
(b) 48 N
(c) 24 N
(d) 12 N
Answer. C

Question. An explosion breaks a rock into three parts in a horizontal plane. Two of them go off at right angles to each other. The first part of mass 1 kg moves with a speed of 12 m  s^–1 and the second part of mass 2 kg moves with 8 m s–1 speed. If the third part flies off with 4 m s^–1 speed, then its mass is
(a) 7 kg
(b) 17 kg
(c) 3 kg
(d) 5 kg 
Answer. D

Question. A person holding a rifle (mass of person and rifle together is 100 kg) stands on a smooth surface and fires 10 shots horizontally, in 5 s. Each bullet has a mass of 10 g with a muzzle velocity of 800 m  s^–1. The final velocity acquired by the person and the average force exerted on the person are
(a) – 0.08 m  s^–1, 16 N
(b) – 0.8 m  s^–1, 8 N
(c) – 1.6 m  s^–1, 16 N
(d) – 1.6 m  s^–1, 8 N
Answer. A

Question. An explosion blows a rock into three parts. Two parts go off at right angles to each other. These two are, 1 kg first part moving with a velocity of 12 m s s^–1 and 2 kg second part moving with a velocity 8 m  s^–1.If the third part flies off with a velocity of 4 m  s^–1, its mass would be
(a) 7 kg
(b) 17 kg
(c) 3 kg
(d) 5 kg 
Answer. D

Question. A mass of 1 kg is thrown up with a velocity of 100 m/s. After 5 seconds, it explodes into two parts.One part of mass 400 g comes down with a velocity 25 m/s. The velocity of other part is (Take g = 10 m  s^–2)
(a) 40 m/s
(b) 80 m/s
(c) 100 m/s
(d) 60 m/s 
Answer. C

Question. A shell, in flight, explodes into four unequal parts.Which of the following is conserved?
(a) Potential energy
(b) Momentum
(c) Kinetic energy
(d) Both (a) and (c).
Answer. B

Question. A man fires a bullet of mass 200 g at a speed of 5 m/s.The gun is of one kg mass. By what velocity the gun rebounds backward?
(a) 1 m/s
(b) 0.01 m/s
(c) 0.1 m/s
(d) 10 m/s.
Answer. A

Question. A body of mass 5 kg explodes at rest into three fragments with masses in the ratio 1 : 1 : 3. The fragments with equal masses fly in mutually perpendicular directions with speeds of 21 m/s. The velocity of heaviest fragment in m/s will be
(a) 7 2
(b) 5 2
(c) 3 2
(d) 2 
Answer. A

Question. Which one of the following statements is incorrect?
(a) Rolling friction is smaller than sliding friction.
(b) Limiting value of static friction is directly proportional to normal reaction.
(c) Frictional force opposes the relative motion.
(d) Coefficient of sliding friction has dimensions of length.
Answer. D 

Question. A conveyor belt is moving at a constant speed of 2 m s^–1. A box is gently dropped on it. The coefficient of friction between them is m = 0.5. The distance that the box will move relative to belt before coming to rest on it, taking g = 10 m s^–2, is
(a) 0.4 m
(b) 1.2 m
(c) 0.6 m
(d) zero
Answer. A

Question. A block of mass 10 kg placed on rough horizontal surface having coefficient of friction m = 0.5, if a horizontal force of 100 N acting on it then acceleration of the block will be
(a) 10 m/s²
(b) 5 m/s²
(c) 15 m/s²
(d) 0.5 m/s²
Answer. B 

Question. On the horizontal surface of a truck a block of mass 1 kg is placed (m = 0.6) and truck is moving with acceleration 5 m/s2 then the frictional force on the block will be
(a) 5 N
(b) 6 N
(c) 5.88 N
(d) 8 N 
Answer. A

Question. A block has been placed on a inclined plane with the slope angle q, block slides down the plane at constant speed. The coefficient of kinetic friction is equal to
(a) sinq
(b) cosq
(c) g
(d) tanq
Answer. D

Question. Consider a car moving along a straight horizontal road with a speed of 72 km/h. If the coefficient of static friction between the tyres and the road is 0.5, the shortest distance in which the car can be stopped is (taking g = 10 m/s²)
(a) 30 m
(b) 40 m
(c) 72 m
(d) 20 m 
Answer. B 

Question. A heavy uniform chain lies on horizontal table top.If the coefficient of friction between the chain and the table surface is 0.25, then the maximum fraction of the length of the chain that can hang over one edge of the table is
(a) 20%
(b) 25%
(c) 35%
(d) 15% 
Answer. A

Question. Starting from rest, a body slides down a 45° inclined plane in twice the time it takes to slide down the same distance in the absence of friction. The coefficient of friction between the body and the inclined plane is
(a) 0.80
(b) 0.75
(c) 0.25
(d) 0.33 
Answer. B  

Question. A block of mass 10 kg is in contact against the inner wall of a hollow cylindrical drum of radius 1 m.The coefficient of friction between the block and the inner wall of the cylinder is 0.1. The minimum angular velocity needed for the cylinder to keep the block stationary when the cylinder is vertical and rotating about its axis, will be (g = 10 m/s²)
(a) 10 π rad/s
(b) √10 rad/s
(c) 10/2π rad/s
(d) 10 rad/s
Answer. D 

Question. Two stones of masses m and 2m are whirled in horizontal circles, the heavier one in a radius r/2 and the lighter one in radius r. The tangential speed of lighter stone is n times that of the value of heavier stone when they experience same centripetal forces.
The value of n is
(a) 4
(b) 1
(c) 2
(d) 3 
Answer. C  

Question. A car is moving in a circular horizontal track of radius 10 m with a constant speed of 10 m/s. A bob is suspended from the roof of the car by a light wire of length 1.0 m. The angle made by the wire with the vertical is
(a) p/3
(b) p/6
(c) p/4
(d) 0°
Answer. C 

Question. A car of mass 1000 kg negotiates a banked curve of radius 90 m on a frictionless road. If the banking angle is 45°, the speed of the car is
(a) 20 m s^–1
(b) 30 m s^–1
(c) 5 m s^–1
(d) 10 m s^–1
Answer. B

Question. A roller coaster is designed such that riders experience “weightlessness” as they go round the top of a hill whose radius of curvature is 20 m. The speed of the car at the top of the hill is between
(a) 16 m/s and 17 m/s
(b) 13 m/s and 14 m/s
(c) 14 m/s and 15 m/s
(d) 15 m/s and 16 m/s
 Answer. C 

Question. A 500 kg car takes a round turn of radius 50 m with a velocity of 36 km/hr. The centripetal force is
(a) 1000 N
(b) 750 N
(c) 250 N
(d) 1200 N
Answer. A 

Question. A ball of mass 0.25 kg attached to the end of a string of length 1.96 m is moving in a horizontal circle. The string will break if the tension is more than 25 N.What is the maximum speed with which the ball can be moved ?
(a) 5 m/s
(b) 3 m/s
(c) 14 m/s
(d) 3.92 m/s. 
Answer. C

Question. When milk is churned, cream gets separated due to
(a) centripetal force
(b) centrifugal force
(c) fricitional force
(d) gravitational force
Answer. B

Question. Two bodies of mass 4 kg and 6 kg are tied to the ends of a massless string. The string passes over a pulley which is frictionless (see figure). The acceleration of the system in terms of acceleration due to gravity (g) is
(a) g
(b) g/2
(c) g/5
(d) g/10
Answer. C 

Question. A person of mass 60 kg is inside a lift of mass 940 kg and presses the button on control panel. The lift starts moving upwards with an acceleration 1.0 m/s². If g = 10 m s^–2, the tension in the supporting cable is
(a) 8600 N
(b) 9680 N
(c) 11000 N
(d) 1200 N
Answer. C

Question. The mass of a lift is 2000 kg. When the tension in the supporting cable is 28000 N, then its acceleration is
(a) 4 m s^–2 upwards
(b) 4 m s^–2 downwards
(c) 14 m s^–2 upwards
(d) 30 m s^–2 downwards
Answer. A  

Question. A block of mass m is placed on a smooth wedge of inclination q. The whole system is accelerated horizontally so that the block does not slip on the wedge. The force exerted by the wedge on the block will be (g is acceleration due to gravity)
(a) mg cosq
(b) mg sinq
(c) mg
(d) mg/cosq 
Answer. D 

Question. A man weighs 80 kg. He stands on a weighing scale 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)
(a) zero
(b) 400 N
(c) 800 N
(d) 1200 N 
Answer. D 

Question. A monkey of mass 20 kg is holding a vertical rope.The rope will not break when a mass of 25 kg is suspended from it but will break if the mass exceeds 25 kg. What is the maximum acceleration with which the monkey can climb up along the rope?
(g = 10 m/s²)
(a) 5 m/s²
(b) 10 m/s²
(c) 25 m/s²
(d) 2.5 m/s²
Answer. D 

Question. A lift of mass 1000 kg which is moving with acceleration of 1 m/s² in upward direction, then the tension developed in string which is connected to lift is
(a) 9800 N
(b) 10,800 N
(c) 11,000 N
(d) 10,000 N
Answer. B 

Question. A mass of 1 kg is suspended by a thread. It is
(i) lifted up with an acceleration 4.9 m/s²,
(ii) lowered with an acceleration 4.9 m/s².
The ratio of the tensions is
(a) 1 : 3
(b) 1 : 2
(c) 3 : 1
(d) 2 : 1
Answer. C 

Question. A monkey is decending from the branch of a tree with constant acceleration. If the breaking strength of branch is 75% of the weight of the monkey, the minimum acceleration with which monkey can slide down without breaking the branch is
(a) g
(b) 3g/4
(c) g/4
(d) g/2
Answer. C