JEE Physics Work Energy and Power MCQs Set B

Question. Two perfectly elastic particles A and B of equal masses travelling along the line joining them with velocity 15 m/s and 10 m/s respectively, collide. Their velocities after the elastic collision will be (in m/s), respectively
(a) 10, 15
(b) 20, 5
(c) 3, 20
(d) 0, 25

Answer: A

Question. Select the false statement
(a) The momentum of a ball colliding elastically with the floor is conserved
(b) In an oblique elastic collision between two identical bodies with initially one of them at rest, final velocities are perpendicular
(c) The coefficient of restitution for a collision between two steel balls lies between zero and one
(d) In elastic collision, kinetic energy during the collision is not conserved

Answer: A

Question. A bullet of mass 20 g leaves a riffle at an initial speed 100 m/s and strikes a target at the same level with speed 50 m/s. The amount of work done by the resistance of air will be
(a) 75 J
(b) 50 J
(c) 25 J
(d) 100 J

Answer: A

Question. A knife of mass m is at a height x from a large wooden block. The knife is allowed to fall freely, strikes the block and comes to rest after penetrating distance y. The work done by the wooden block to stop the knife is
(a) – mg (x + y)
(b) mg (x – y)
(c) – mgy
(d) mgx

Answer: A

Question. If net force on a system is zero then
(a) All of these
(b) The acceleration of its a constituent particle may be non-zero
(c) Its kinetic energy may increase
(d) Its momentum is conserved

Answer: A

Question. Internal forces acting within a system of particles can alter
(a) The kinetic energy of the system, but not the linear momentum of the system
(b) Neither linear momentum nor kinetic energy of the system
(c) The linear momentum of the system, but not the kinetic energy of the system
(d) The linear momentum as well as the kinetic energy of the system

Answer: A

Question. When a conservative force does positive work on a body, then the
(a) Potential energy of body decreases
(b) Total mechanical energy of body decreases
(c) Total mechanical energy of body increases
(d) Potential energy of body increases

Answer: A

Question. The force required to row a boat at constant velocity is proportional to square of its speed. If a speed of v km/h requires 4 kW, how much power does a speed of 2v km/h require?
(a) 32 kW
(b) 24 kW
(c) 16 kW
(d) 8 kW

Answer: A

Question. Two balls of masses m each are moving at right angle to each other with velocities 6 m/s and 8 m/s respectively. If collision between them is perfectly inelastic, the velocity of combined mass is
(a) 5 m/s
(b) 2.5 m/s
(c) 10 m/s
(d) 15 m/s

Answer: A

Question. Two bodies with kinetic energies in the ratio of 4 : 1 are moving with equal linear momentum. The ratio of their masses is
(a) 1 : 4
(b) 1 : 2
(c) 1 : 1
(d) 4 : 1

Answer: A

Question. If kinetic energy of a body is increased by 300% then percentage change in momentum will be
(a) 100%
(b) 150%
(c) 265%
(d) 73.2%

Answer: A

Question. A bomb of mass 30 kg at rest explodes into two pieces of masses 18 kg and 12 kg. The velocity of 18 kg mass is 6 ms^–1. The kinetic energy of the other mass is
(a) 486 J
(b) 324 J
(c) 256 J
(d) 524 J

Answer: A

Question. A shell of mass 200 gm is ejected from a gun of mass 4 kg by an explosion that generates 1.05 kJ of energy. The initial velocity of the shell is
(a) 100 ms^–1
(b) 120 ms^–1
(c) 80 ms^–1
(d) 40 ms^–1

Answer: A

Question. A body dropped from a height h with initial velocity zero, strikes the ground with a velocity 3 m/s. Another body of same mass is thrown from the same height h with an initial velocity of 4 m/s. Find the final velocity of second mass, with which it strikes the ground.
(a) 3 m/s
(b) 12 m/s
(c) 4 m/s
(d) 5 m/s

Answer: A

Question. The potential energy of a system increases if work is done
(a) By the system against a conservative force
(b) Upon the system by a conservative force
(c) Upon the system by a non-conservative force
(d) By the system against a non-conservative force

Answer: A

Question. A car moving with a speed of 40 km/h can be stopped by applying brakes after at least 2 m. If the same car is moving with a speed of 80 km/h, what is the minimum stopping distance?
(a) 8 m
(b) 2 m
(c) 6 m
(d) 4 m

Answer: A

Question. A child is sitting on a swing. Its minimum and maximum heights from the ground are 0.75 m and 2 m respectively, its maximum speed will be
(a) 5 m/s
(b) 10 m/s
(c) 8 m/s
(d) 15 m/s

Answer: A

Question. A child is sitting on a swing. Its minimum and maximum heights from the ground are 0.75 m and 2 m respectively, its maximum speed will be
(a) 5 m/s
(b) 10 m/s
(c) 8 m/s
(d) 15 m/s

Answer: A