Force of Friction

MCQs Part 3

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.

  1. KA = KC, hA = hC
  2. KB > KC, hA = hC
  3. KB > KC, hA < hc
  4. KB > KC, hA > hC

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)—

  1. tension in the string is 40 N
  2. displacement of the block in the given time interval is 2 m
  3. work done by gravity is _ 20 J
  4. work done by tension is 80 J

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—

  1. the path taken
  2. the time taken
  3. the weight of the box
  4. the frame of reference

Answer: (a) the path taken
(b) the time taken

Question 24: When a force is applied to a moving body,

  1. both momentum and K.E. of the body may change
  2. neither momentum nor K.E. of the body changes
  3. its momentum may change but K.E. may remain constant
  4. its momentum may remain constant but K.E. may change

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—

  1. lifting force is positive
  2. lifting force is negative
  3. force of gravity is positive
  4. force of gravity is negative

Answer: (a) lifting force is positive
(d) force of gravity is negative

Question 27: In an elastic collision—

  1. KE remains constant
  2. linear momentum remains constant
  3. final K.E. = initial K.E.
  4. final linear momentum = initial linear momentum

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—

  1. resultant force on the particle must be parallel to the velocity at all instants
  2. the resultant force on the particle must be at an angle less than 90º all the time
  3. magnitude of its linear momentum is increasing continuously
  4. its height above the ground must decrease continuously

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—

  1. time taken in doing so
  2. path chosen
  3. weight of the body
  4. height of the table

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—

  1. total energy of the ball and the earth remains the same
  2. total momentum of the ball and the earth is conserved
  3. momentum of the ball just after the collision is same as that just before the collision
  4. mechanical energy of the ball remains the same during the collision

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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