Question

A boy tied a string to one of the ends of a box and started sliding on a circular track and completed half revolution. The work done by friction on the box is _____.

• A. positve
• B. zero
• C. negative
• D. can't be determined.

Answer 1

The correct option is C negative

Friction is a non-conservative force and the work done by it depends on the path taken. In the above case, friction is always acting in the direction opposite to motion.

Work done = $F\times S\times cos\theta$, where F and S are force and displacement respectively and $\theta$ is the angle between the force and the displacement.

In the above case, $\theta$ is ${180}^{\circ }$ and the work done will be always negative.