Question

A smooth rod op is fixed vertically. A disc of mass m and radius r is rolling without slipping on a rough horizontal surface as shown. Velocity of centre of mass of disc is o v . A rod ab of length l is connected with disc at a, 2 r distance vertically up from centre of disc with pin joint (about which it can rotate freely), other end of the rod is attached to a small smooth ring b , which can move freely over rod op . At an instant rod ab makes an angle 60o with the vertical. The velocity of ring on the vertical rod at this instant is

Answer 1

Only translational motion is present.

option (A) is correct.

Explanation:

Question statement:

As shown in the figure, a uniform disc of mass m is rolling without slipping with a angular velocity. The portion AB is rough and BC is smooth. When it crosses point B disc will be in:

(A) Translatory motion only

(B) Pure rolling motion

(C) Rotational motion only

(D) None of the above

Solution:

Since the body is rolling on the rough surface, friction does not act.

On the smooth surface, Since no external torque, and forces are present , it continuous to roll. Hence only translational motions is present.