Q7.29 Explain why friction is necessary to make the disc in Fig. 7.41 roll in the direction indicated
(a) Give the direction of frictional force at , and the sense of frictional torque, before perfect rolling begins.
Since the velocity at point B is tangentially leftward so the frictional force will act in the rightward direction.
The sense of frictional torque is perpendicular (outward) to the plane of the disc.
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