Question 21: The ball rolls down without slipping (which is at rest at A) along AB having friction. It rolls to a maximum height hc where BC has no friction. KA, KB and KC are kinetic energies at A, B and C.
Answer: (d) KB > KC, hA > hC
Question 22: A block of mass 2 kg is hanging over a smooth and light pulley through a light string. The other end of the string is pulled by a constant force F = 40 N. The kinetic energy of the block increases by 40 J in a given interval of time. Then (Take g = 10 ms_2)
Answer: (a) tension in the string is 40 N
(b) displacement of the block in the given time interval is 2 m
(c) work done by gravity is _ 20 J
Question 23: You lift a box from the floor and keep it on a table. The work done by you on the box does not depend on
Answer: (a) the path taken
(b) the time taken
Question 24: When a force is applied to a moving body,
Answer: (a) both momentum and K.E. of the body may change
(c) its momentum may change but K.E. may remain constant
Question 25: A vehicle is driven along a straight horizontal track by a motor which exerts a constant driving force. The vehicle starts from rest at t = 0 and the effect of friction and air resistance are negligible. If kinetic energy of vehicle at time t is E and power developed by the motor is P, which of the graphs given below is/are correct?
Answer:(a)
(c)
Question 26: When a body is moving vertically upward with a constant speed, work done by
Answer: (a) lifting force is positive
(d) force of gravity is negative
Question 27: In an elastic collision
Answer: (b) linear momentum remains constant
(c) final K.E. = initial K.E.
(d) final linear momentum = initial linear momentum
Question 28: KE of a particle increases continuously with time when
Answer: (b) the resultant force on the particle must be at an angle less than 90º all the time
(c) magnitude of its linear momentum is increasing continuously
Question 29: When you carry a body from floor and keep it on table, work done does not depend on
Answer: (a) time taken in doing so
(b) path chosen
Question 30: A ball hits a floor and rebounds after an inelastic collision. In this case
Answer: (a) total energy of the ball and the earth remains the same
(b) total momentum of the ball and the earth is conserved
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