CBSE Class 11 Physics Laws of Motion MCQs Set 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: 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: 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: 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 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 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 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 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: 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^–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 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: Three blocks with masses m, 2m and 3m are connected by strings, as shown in the figure. After an upward force F is applied on block m, the masses move upward at constant speed v. What is the net force on the block of mass 2m? (g is the acceleration due to gravity)
a) 3mg
b) 6mg
c) zero
d) 2mg
Answer: c

Question:Two particles of equal mass are connected to a rope AB of negligible mass, such that one is at end A and the other dividing the length of the rope in the ratio 1 : 2 from B. The rope is rotated about end B in a horizontal plane. Ratio of the tensions in the smaller pa1t to the other is (ignore effect of gravity)
a) 4 : 3
b) l : 4
c) 1 : 2
d) 1 : 3
Answer: d

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: The engine of a car produces an acceleration of 6 ms^-2 in the car. If this car pulls another car of the same mass, then the acceleration would be
a) 6ms^-2
b) 12ms^-2
c) 3ms^-2
d) l.5ms^-2
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 surface with a vertical cross-section given by y = x³ I 6. If the coefficient of friction is 0.5, the maximum height above the ground at which the block can be placed without slipping is. 
a) (1/6) m
b) (2/3) m
c) (1/3) m
d) (1/2) m
Answer: a

Question:A block of mass 2 kg is at rest on a floor. The coefficient of static friction between block and the floor is 0.54. A horizontal force of 2.8 N is applied to the block. What should be the frictional force between the block and the floor? (take,g = 10 m/s²)
a) 8.8N
b) 5.8N
c) 2.8N
d) JO.SN
Answer: c

Question: Starting from rest, the time taken by a body sliding down on a rough inclined plane at45° with the horizontal is twice the time taken to travel on a smooth plane of same inclination and same distance. Then, the coefficient of kinetic friction is
a) 0.25
b) 0.33
c) 0.50
d) 0.75
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 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 block of mass 2 kg rests on a horizontal surface. If a horizontal force of 5 N is applied on the block, the frictional force on it is (take,μ k = 0.4, μ s = 0.5)
a) 5 N
b) 10 N
c) 8 N
d) zero
Answer: c

Question:A body is coming with a velocity of 72 kmh^-1 on a rough horizontal surface of coefficient of friction 0.5. If the acceleration due to gravity is 10 ms ^-2, find the minimum distance, it can be stopped.
a) 400 rn
b) 40 m
c) 0.40 rn
d) 4 m
Answer: b

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 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:The resultant of two forces acting at an angle of I 20° is 10 kg-wt and is perpendicular to one of the forces. That force is
a) 10/✓3kg-wt
b) I0kg - wt
c) 20✓3 kg-wt
d) 10✓3 kg-wt
Answer: a

Question: Sand is being dropped on a conveyer belt at the rate of M kg/s. The force necessary to keep the belt moving with a constant velocity of v m/s will be
a) Mv /2 newton
b) zero
c) Mv newton
d) 2 Mv newton
Answer: c

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:A piece of wire is bent in the shape of a parabola y = kx² (y-axis vertical) with a bead of mass m on it. The bead can slide on the wire without friction. It stays at the lowest point of the parabola when the wire is at rest. The wire is now accelerated parallel to the x-axis with a constant acceleration a. The distance of the new equilibrium position of the bead, where the bead can stays at rest with respect to the wire, from the y -axis is(
a) a/g k
b) a/2gk
c) 2a/gk
d) a/4gk
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 p rad/s
b) 10 rad/s
c) 10 /2π rad/s
d) 10 rad/s
Answer: d