Question

In which of the following options is the frictional force working?

• A. A boulder rolling down a mountain
• B. Airplane flying
• C. A swimmer in river
• D. None of these

Answer 1

Answer: (A), (B), (C)

The correct options are
A

A boulder rolling down a mountain

B

Airplane flying

C

A swimmer in river

Friction is present whenever there is contact between two surfaces. In the first three options given here, friction is experienced as there is contact between two surfaces.

But when the Moon is revolving around the Earth there is no contact between the surfaces of the Moon and the Earth. Also, the Moon orbits in space where there is vacuum. Hence, no frictional force is involved in this case.