Question

A force $F$ acts tangentially at the highest point of a hollow sphere of mass $m$ kept on a rough horizontal plane. If the sphere rolls without slipping then,

• A. Static friction will act on the sphere towards left.
• B. Kinetic friction will act on the sphere toward right.
• C. Static friction will act on the sphere toward right.
• D. Kinetic friction will act on the sphere toward left.

Answer 1

The correct option is C Static friction will act on the sphere toward right.

The force $\left(F\right)$ causes angular acceleration apart from causing linear acceleration. The force has dual role to play in this case. As far as its rotational form (torque) is concerned, resulting angular acceleration means that angular velocity tends to increase. This, in turn, induces tendency of the rolling body to slide in the backward direction (i.e. in the opposite direction of force). Force of friction, therefore, appears in the direction of external force to check the sliding tendency.