CBSE Class 11 Physics Law of Motion Assignment

Question. When a body is stationary
(a) there is no force acting on it
(b) the forces acting on its are not in contact with it
(c) the combination of forces acting on it balance each other
(d) the body is in vacuum
Answer.C

Question. A force of 50 N is required topush a car on a level road with constant speed of 10 m/s. The mass of the car is 500 kg. What force should be applied to make the car accelerate at 1 m/s² ?
(a) 550 N
(b) 450 N
(c) 500 N
(d) 2500 N
Answer.A

Question. A ship of mass 3 × 10⁷ kg initially at rest is pulled by a force of 5 × 10⁴ N through a distance of 3 m. Assuming that the resistance due to water is negligible, what will be the speed of the ship ?
(a) 0.1 m/s
(b) 1.5 m/s
(c) 5 m/s
(d) 0.2 m/s
Answer.A

Question. A constant force acts on a body of mass 0.9 kg at rest for 10 s. If the body moves a distance of 250 m, the magnitude of the force is
(a) 3 N
(b) 3.5 N
(c) 4 N
(d) 4.5 N
Answer.D

Question. In the above problem, if a push of 5 N is applied on the lighter mass, the force exerted by the lighter mass on the heavier mass will be
(a) 5 N
(b) 4 N
(c) 2 N
(d) None of the above
Answer.D

Question. If a body loses half of its velocity on penetrating 3 cm in a wooden block, them how much will it penetrate more before coming to rest ?
(a) 1 cm
(b) 2 cm
(c) 3 cm
(d) 74 N
Answer.A

Question. In the game of tug of wars, a condition of equilibrium exists. Both the teams pull the rope with a force of 10⁴N.The tension in the rope is
(a) 2 × 10⁴ N
(b) 0
(c) 10⁴ N
(d) none
Answer.C

Question. A 50 kg boy stands on a plateform spring scale in a lift that is going down with a constant speed 3 m/s. If the lift is brought to rest by a constant deceleration in a distance of 9 m, what does the scale read during this period ?  (g = 9.8 m/s²)
(a) 500 N
(b) 465 N
(c) 515 N
(d) zero
Answer.C

Question. Ten coins are placed on top of each other on a horizontal table. If the mass of each coin is 10 g and acceleration due to gravity is 10 ms–2, what is the magnitude and direction of the force on the 7th coin (counted from the bottom) due to all the coins above it ?
(a) 0.3 N downwards
(b) 0.3 N upwards
(c) 0.7 N downwards
(d) 0.7 N upwards
Answer.A

Question. A sphere is accelerated upwards with the help of a cord whose breaking strength is five times its weight. The maximum acceleration with which the sphere can move up without cord breaking is
(a) 4g
(b) 3g
(c) 2g
(d) g
Answer.A

Question. A body of mass m is acted upon by a force F and the acceleration produced is a. If three forces each equal to F and inclined to each other at 120o act on the same body, the acceleration produced will be
(a) a/√ 3
(b) 2a
(c) 3a
(d) zero
Answer.D

Question. An object is resting at the bottom of two strings which are inclined at an angle of 120° with each other. Each string can withstand a tension of 20 N. The maximum weight of the object that can be sustained without breaking the string is :
(a) 10 N
(b) 20 N
(c) 20 2 N
(b) 40 N
Answer.B

Question. A monkey is accelerating down a string whose breaking strength is two third of his weight. The minimum acceleration of the monkey should be
(a) 0
(b) 2/3 g
(c) g
(d) g/3
Answer.D

Question. A lift weighing 1000 kg is moving upwards with an acceleration of 1 m/s². The tension in the supporting cable is
(a) 980 N
(b) 10800 N
(c) 9800 N
(d) 8800 N
Answer.B

Question. In an elevator moving vertically up with an acceleration ‘g’, the force exerted on the floor by a passenger of mass M is
(a) Mg
(b) 1/2 Mg
(c) zero
(d) 2 Mg
Answer.D

Question. The mass of a lift is 500 kg. What will be the tension in its cable when it is going up with an acceleration of 2.0 m/s² ?
(a) 5000 N
(b) 5600 N
(c) 5900 N
(d) 6200 N
Answer.C

Question. A man weighs 80 kg. He stands on a weighing scale in the 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. In the above question normal reaction between ground and wedge will have magnitude equal to :
(a) N cos θ + Mg
(b) N cos θ + Mg + mg
(c) N cos θ – Mg
(d) N sin θ + Mg + mg
Answer.A

Question. The pendulum hanging from the ceiling of a railway carriage makes angle 30° with the vertical, when it is accelerating.
The acceleration of the carriage is :
(a) √3/2 g
(b) √2/3 g
(c) g√3
(d) g/√3
Answer.D

Question. A block is placed on the top of a smooth inclined plane of inclination θ kept on the floor of a lift. When the lift is descending with a retardation a, the block is released. The acceleration of the block relative to the incline is :
(a) g sin θ
(b) a sin θ
(c) (g –a) sin θ
(d) (g + a) sin θ
Answer.D

Question. A block of mass m is placed on a smooth wedge of inclination θ. 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 (g is acceleration due to gravity) will be
(a) mg
(b) mg/cos θ
(c) mg cos θ
(d) mg sin θ
Answer.B

Question. A wooden box of mass 8 kg slides down an inclined plane of inclination 30° to the horizontal with a constant acceleration of 0.4 ms^–2. What is the force of friction between the box and inclined plane ? (g = 10 m/s²)
(a) 36.8 N
(b) 76.8 N
(c) 65.6 N
(d) None of these
Answer.A

Question. A body is projected along a rough horizontal surface with a velocity 6 m/s. If the body comes to rest after travelling 9 m, then coefficient of sliding friction, is : (g = 10 m/s²)
(a) 0.5
(b) 0.4
(c) 0.6
(d) 0.2
Answer.D

Question. A block of mass 5 kg is kept on a horizontal floor having coefficient of friction 0.09. Two mutually perpendicular horizontal forces of 3 N and 4 N act on this block. The acceleration of the block is : (g = 10 m/s²)
(a) zero
(b) 0.1 m/s²
(c) 0.2 m/s²
(d) 0.3 m/s²
Answer.B

Question. A minimum force F is applied to a block of mass 102 kg to prevent it from sliding on a plane with an inclination angle 30° with the horizontal. If the coefficients of static and kinetic friction between the block and the plane are 0.4 and 0.3 respectively, then the force F is :
(a) 157 N
(b) 224 N
(c) 315 N
(d) zero
Answer.A

Question. The upper half of an inclined plane of inclination θ is perfectly smooth while the lower half rough. A block starting from rest at the top of the plane will again come to rest at the bottom, if the coefficient of friction between the block and the lower half of the plane is given by :
(a) μ = 2 tan θ
(b) μ = tan θ
(c) μ = 2 / tan θ
(d) μ =1 / tan θ
Answer.A

Question. A block is gently placed on a conveyor belt moving horizontally with constant speed. After t = 4 s, the velocity of the block becomes equal to velocity of the belt. If the coefficient of friction between the block and the belt is μ = 0.2, then the velocity of the conveyor belt is
(a) 8 m/s
(b) 6 m/s
(c) 4 m/s
(d) 2 m/s
Answer.A

Question. If a block moving up at θ = 30o with a velocity 5 m/s, stops after 0.5 sec, then μ is
(a) 0.5
(b) 1.25
(c) 0.6
(d) none of the above.
Answer.C

Question. A car having a mass of 1000 kg is moving at a speed of 30 m/s. Brakes are applied to bring the car to rest. If the frictional force between the tyres and the road surface is 5000 N, the car will come to rest in
(a) 5 s
(b) 8 s
(c) 12 s
(d) 6 s
Answer.D

Question. Which of the following statements is true in a tug of war.
(a) The team which applies a greater force on the rope than the other wins.
(b) The team which applies a smaller force on the other wins.
(c) The team which pushes harder against the ground wins.
(d) none of these
Answer.B

Question. A block of mass 4 kg is placed on a rough horizontal plane.A time dependent force F = kt2 acts on the block, where k = 2N/s². Coefficient of friction θ = 0.8. Force of friction between block and the plane at t = 2 s is :
(a) 8 N
(b) 4 N
(c) 2 N
(d) 32 N
Answer.B

Question. The coefficient of friction between the tyres and road is 0.4. The minimum distance covered before attaining a speed of 8 m/s starting from rest is nearly : (g = 10 m/s²)
(a) 8.0 m
(b) 4.0 m
(c) 10.0 m
(d) 16.0 m
Answer.A

Question. A block of mass 0.1 kg is held against a wall applying horizontal force of 5 N on the block. If coeff. of friction between the block and the wall is 0.5, the magnitude of frictional force acting on the block is
(a) 2.5 N
(b) 0.49 N
(c) 0.98 N
(d) 4.9 N
Answer.C

Question. A box of mass 8 kg is placed on a rough inclined plane of inclination θ. Its downward motion can be prevented by applying an upward pull F and it can be made to slide upwards by applying a force 2 F. The coefficient of friction between the box and the inclined plane is :
(a) 1/3 tan θ
(b) 3 tan θ
(c) 1/2 tan θ
(d) 2 tan θ
Answer.A

Question. The coefficient of friction of a surface is 1/√3 . What should be the angle of inclination so that a body placed on the surface just begins to slide down ?
(a) 30^o
(b) 45^o
(c) 60^o
(d) 90^o
Answer.A

Question. In a situation the contact force by a rough horizontal surface on a body placed on it has constant magnitude. If the angle between this force and the vertical is decreased, the frictional force between the surface and the body will
(a) increase
(b) decrease
(c) remain the same
(d) may increase or decrease
Answer.B

Question. While walking on ice, one should take small steps to avoid slipping. This is because smaller steps ensure
(a) larger friction
(b) smaller friction
(c) larger normal force
(d) smaller normal force
Answer.B

Question. Two cars of unequal masses use similar tyres. If they are moving at the same initial speed, the minimum stopping distance
(a) is smaller for the heavier car
(b) is smaller for the lighter car
(c) is same for both car
(d) depends on the volume of the car
Answer.C

Question. A block A kept on an inclined surface just begins to slide if the inclination is 30°. The block is replaced by another block B and it is found that it just begins to slide if the inclination is 40°.
(a) mass of A > mass of B
(b) mass of A < mass of B
(c) mass of A = means of B
(d) all the three are possible
Answer.D

Question. A lift is moving down with acceleration a. A man in the lift drops a ball inside the lift. The acceleration of the ball as observed by the man in the lift and a man standing stationary on the ground are respectively 
(a) g, g
(b) g – a, g – a
(c) g – a, g
(d) a, g
Answer.C

Question. Two forces are such that the sum of their magnitudes is 18 N and their resultant which has magnitude 12 N, is perpendicular to the smaller force. Then the magnitude of the forces are :
(a) 12 N, 6 N
(b) 13 N, 5 N
(c) 10 N, 8 N
(d) 16 N, 2 N
Answer.B

Question. A light string passing over a smooth light pulley connects two blocks of masses m₁ and m₂ (vertically). If the acceleration of the system is g/8, then the ratio of the masses is : 
(a) 8 : 1
(b) 9 : 7
(c) 4 : 3
(d) 5 : 3
Answer.B

Question. A spring balance is attached to the ceiling of a lift. A man hangs his bag on the spring and the spring reads 49 N,when the lift is stationary. If the lift moves downward with an acceleration of 5 ms^–2, the reading of the spring balance will be : 
(a) 24 N
(b) 74 N
(c) 15 N
(d) 49 N
Answer.A

Question. A marble block of mass 2 kg lying on ice when given a velocity of 6 ms^–1 is stopped by friction in 10 s. Then the coefficient of friction is 
(a) 0.02
(b) 0.03
(c) 0.06
(d) 0.01
Answer.C

Question. A light spring balance hangs from the hook of the other light spring balance and a block of mass M kg hangs from the former one. Then the true statement about the scale reading is :
(a) Both the scales read M kg each
(b) The scale of the lower one reads M kg and of the upper one zero
(c) The reading of the two scale can be anything but the sum of the readings will be M kg
(d) Both the scale read M/2 kg
Answer.A

Question. A rocket with a lift-off mass 3.5 × 10⁴ kg is blasted upwards with an initial acceleration of 10 ms^–2. Then the initial thrust of the blast is : 
(a) 3.5 × 10⁵ N
(b) 7.0 × 10⁵ N
(c) 14.0 × 10⁵ N
(d) 1.75 × 10⁵ N
Answer.A

Question. A machine gun fires a bullet of mass 40 g with a velocity 1200 ms^–1. The man holding it, can exert a maximum force of 144 N on the gun. How many bullets can be fire per second at the most ?
(a) 1
(b) 4
(c) 2
(d) 3
Answer.D

Question. Consider a car moving on a straight road with a speed of 100 ms^–1. The distance at which car can be stopped, is [μ_k = 0.5] 
(a) 800 m
(b) 1000 m
(c) 100 m
(d) 400 m
Answer.B

Question. A particle of mass 0.3 kg is subjected to a force F = – kx with k = 15 Nm^–1. What will be its initial accleration, if it is released from a point 20 cm away the origin ? 
(a) 3 ms^–2
(b) 15 ms^–2
(c) 5 ms^–2
(d) 10 ms^–2
Answer.D

Question. The upper half of an inclined plane with inclination Φ is perfectly smooth, while the lower half is rough. A body starting from rest at the top will again come to rest at the bottom, if the coefficient of friction for the lower half is given by
(a) 2 sin Φ
(b) 2 cos Φ
(c) 2 tan Φ
(d) tan Φ
Answer.C

Question. A player caught a cricket ball of mass 150 g moving at a rate of 20 m/s. If the catching process is completed in 0.1 s,the force of the blow exerted by the ball on the hand of the player is equal to 
(a) 150 N
(b) 3 N
(c) 30 N
(d) 300 N
Answer.C

Question. A block A of mass 4 kg is placed on another block B of mass 5 kg, and the block B rests on a smooth horizontal table. If the minimum force that can be applied on A so that both the blocks move together is 12 N, the maximum force that can be applied on B for the blocks to move together will be: 
(a) 30 N
(b) 25 N
(c) 27 N
(d) 48 N
Answer.C

Question. A 4 g bullet is fired horizontally with a speed of 300m/s into 0.8 kg block of wood at rest on a table. If the coefficient of friction between the block and the table is 0.3, how far will the block slide approximately? 
(a) 0.379 m
(b) 0.569 m
(c) 0.758 m
(d) 0.19 m
Answer.A

Question. When a bird of weight W sits on a stretched wire, the tension T in the wire is
(a) > W/2
(b) = W
(c) < W
(d) None of these
Answer.A

Question. A person swimming in a fresh water pool is obeying :
(a) Newton’s second law
(b) Gravitational law
(c) Newton’s third law
(d) Newton’s first law
Answer.B

Question. The passenger move forward when train stops, due to :
(a) inertia of passenger
(b) inertia of train
(c) gravitation pull by earth
(d) none of the above
Answer.B

Question. A mass of 3 kg descending vertically downward supports a mass of 2 kg by means of a light string passing over a pulley. At the end of 5 s the string breaks. How much high from now the 2 kg mass will go ? (g = 9.8 m/s²)
(a) 4.9
 (b) 9.8 m
(c) 16.9 m
(d) 2.45 m
Answer.D