Question

A solid sphere rolls purely down an inclined plane such that it gains angular speed with time. What is the direction of frictional force on the sphere?

• A. Downwards along the incline
• B. Upwards along the incline
• C. zero
• D. Sometimes upwards and sometimes downwards.

Answer 1

The correct option is B Upwards along the incline

The sphere gains angular speed in anti-clockwise direction as it falls along the incline.
It implies that frictional force has to act upwards along the incline to provide the required torque as there is no other force in the picture that can do this. Think!