question_answer

When a body roils without sliding up an inclined plane, the frictional force is

A)  directed up the plane                   

B)  directed down the plane

C)  zero

D)  dependent on its velocity

Correct Answer: A

Solution :

 Since, the body rolls without sliding. \[{{a}_{p}}=0\] and \[{{v}_{p}}=0\] \[\Rightarrow \]            \[V-r\omega =0\] and \[a-r\alpha =0\] \[\Rightarrow \]            \[v=r\omega \] and \[a=r\,\alpha \] Since, the body acceleration 'a' is downwards parallel to the plane. Therefore, acceleration of the body must be in anti-clockwise sense. That means the friction must act up the plane to produce an anti-clockwise torque to produce anti-clockwise angular acceleration.