Systems of Particles and Rotational Motion
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Question : 32
Total: 33
Read each statement below carefully, and state, with reasons, if it is true or false;
(a) During rolling, the force of friction acts in the same direction as the direction of motion of the CM of the body.
(b) The instantaneous speed of the point of contact during rolling is zero.
(c) The instantaneous acceleration of the point of contact during rolling is zero.
(d) For perfect rolling motion, work done against friction is zero.
(e) A wheel moving down a perfectly frictionless inclined plane will undergo slipping (not rolling) motion.
(a) During rolling, the force of friction acts in the same direction as the direction of motion of the CM of the body.
(b) The instantaneous speed of the point of contact during rolling is zero.
(c) The instantaneous acceleration of the point of contact during rolling is zero.
(d) For perfect rolling motion, work done against friction is zero.
(e) A wheel moving down a perfectly frictionless inclined plane will undergo slipping (not rolling) motion.
Solution:
(a) It is true. During rolling, the force of friction acts in the same direction as the direction of motion of the C.M. of the body.
(b) It is true. A rolling body can be imagined to be rotating about an axis passing through the point of contact of the body with the ground and hence its instantaneous speed is zero.
(c) It is false. Since the body is rotating, its instantaneous acceleration is not zero.
(d) It is true. In case of perfect rolling, work done against friction is zero as point of contact does not move.
(e) It is true. A body rolls due to the force of friction acting on it. If the wheel is moving down a perfectly frictionless inclined plane, it will be under the effect of its weight only. Since the weight of the wheel acts along the vertical through its centre of mass, the wheel will not rotate. It will keep on slipping.
(b) It is true. A rolling body can be imagined to be rotating about an axis passing through the point of contact of the body with the ground and hence its instantaneous speed is zero.
(c) It is false. Since the body is rotating, its instantaneous acceleration is not zero.
(d) It is true. In case of perfect rolling, work done against friction is zero as point of contact does not move.
(e) It is true. A body rolls due to the force of friction acting on it. If the wheel is moving down a perfectly frictionless inclined plane, it will be under the effect of its weight only. Since the weight of the wheel acts along the vertical through its centre of mass, the wheel will not rotate. It will keep on slipping.
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