Question

A stone is tied to a string and whirled in a circular path.The work done by the stone is

• A. negative
• B. zero
• C. positive
• D. none of the above

Answer 1

The correct option is B

zero

Explanation for the correct option.

B: zero

1. In a circular motion when the body moves with a uniform speed then only centripetal force acts on it and it acts in the direction towards the center of the circular path.
2. The direction of force is perpendicular to the direction of motion and the angle between the force and displacement is 90°.

W = F x S x cos ∅

W = F x s x cos 90°

W = 0

Explanation for the incorrect options.

A: negative

Work done is negative only when,

90° < ∅ < 180° and cos ∅ < 0 i.e W < 0.
C: positive

Work doen is positive only when,

0° < ∅ < 90° and cos ∅ > 0 i.e W > 0.
D: none of the above.

Thus, work done by stone is zero.