(i) Explain why friction is necessary to make the disc to roll in the direction indicated. (ii) Give the direction of frictional force at `B`, and the sense of frictional torque, before perfect rolling begins. (iii) What is the force of friction after perfect rolling begins?

(i) Explain why friction is necessary to make the disc to roll in the

1.	(i) Explain why friction is necessary to make the disc to roll in the direction indicated. (ii) Give the direction of frictional force at `B`, and the sense of frictional torque, before perfect rolling begins. (iii) What is the force of friction after perfect rolling begins?
Answer» (i) To roll a disc, a torque is required which in turn requires a tangential force to on it. As the force of friction is the only tangential force acting on the disc, so it is necessarily required for the rolling of a disc. (ii) Frictional force at `B` opposes the velocity of `B`. therefore, frictional force is in the same direction as the arrow. the sence of frictional torque is such as to oppose the angular motion. by right hand rule, `vec(omega)_(0)` act into the plane of paper and `vec(tau)` out of the paper. (iii) frictional force decreases the velocity of the point of constant `B`. perfect rolling begins when this velocity is zero at which the force of friction is zero.

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(i) Explain why friction is necessary to make the disc to roll in the direction indicated. (ii) Give the direction of frictional force at `B`, and the sense of frictional torque, before perfect rolling begins. (iii) What is the force of friction after perfect rolling begins?

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