Force of Friction

MCQs (Part 2)

Question 11: If a body loses half its velocity on penetrating 3 cm in a wooden block, then how much will it penetrate more before coming to rest?

  1. 1 cm
  2. 2 cm
  3. 3 cm
  4. 4 cm

Answer: (a) 1 cm

Explanation: Let a be the retradation. From

Let the further distance travelled be s'.

From

Question 12: A wire suspended vertically from one of its ends is stretched by attaching a weight of 200 N to the lower end. The weight stretches the wire by 1 mm. Then the elastic energy stored in the wire is

  1. 0.2 J
  2. 10 J
  3. 20 J
  4. 0.1 J

Answer: (d) 0. 1 J

Explanation:

Elastic potential energy joule.

Question 13: Velocity time graph of a particle of mass 2 kg moving in a straight line is as shown in Fig. Work done by all forces on the particle is—

  1. 400 J
  2. - 400 J
  3. - 200 J
  4. 200 J

Answer: (b) - 400 J

Explanation: Initial velocity of particle,

Final velocity of the particle,

According to work energy theorem,

K.E. = Kf _ Ki

Question 14: A particle of mass m is projected with velocity u at an angle a with horizontal. During the period, when the particle descends from highest point to the position, where its velocity vector makes an angle a/2 with horizontal, work done by gravity is

Answer: (d)

Explanation: Horizontal component of velocity remains unchanged throughout

Question 15: A particle of mass 0.1 kg is subjected to a force which varies with distance as shown in Fig. If it starts its journey from rest at x = 0, its velocity at x = 12 m is—

Answer: (b)

Question 16: A particle, which is constrained to move along x-axis , is subjected to a force in the same direction which varies with the distance x of the particle from the origin as Here k and a are positive constants. For the functional form of the potential energy of the particle is—

Answer: (d)

Question 17: A car moving with a velocity of 50 km/h can be stopped by brakes after at least 6m. If the same car is moving at a speed of 100 km/h, the minimum stopping distance is—

  1. 12 m
  2. 18 m
  3. 24 m
  4. 6 m

Answer: (c) 24 m

Question 18: A particle is placed at the origin and a force
F = kx is acting on it (where k is a positive constant). If U (0) = 0, the graph of U(x) versus x will be (where U is the potential energy function)—

Answer: (a)

Question 19: A ball, whose K.E. is E, is projected at an angle of 45º to the horizontal. The kinetic energy of the ball at the highest point of its flight will be—

  1. E
  4. Zero

Answer: (c)

Question 20: A stone tied to a string of length L is whirled in a vertical circle with the other end of the string at the centre. At a certain instant of time, the stone is at its lowest position and has a speed u. The magnitude of the change in its velocity as it reaches a position, where the string is horizontal, is—

Answer: (d)

Copyright © excellup 2014