Question

When a body is whirled in circular motion, the work done on it is:
A. Positive
B. Negative
C. Zero
D. Infinite

Answer 1

Hint: In this question we are asked to calculate the work done on a body when it is whirled in a circular motion. As the object is in circular motion, we shall discuss the circulation motion and the formula used to calculate the work done on an object in circular motion. While doing so we shall also discuss the nature of force on the object.

Complete answer:
We know that when an object is whirled in circulation, the centripetal force is present. The direction of this centripetal force is always toward the centre of the circular path followed by the object. Now, we also know that, during a circular motion of an object, the velocity of the object is always tangential, which makes the distance moved by the object in a perpendicular direction with the centripetal force.
Now, we know that the work done is given as,
\[W=Fs\cos \theta \]

              

Where, \[\theta \] is the angle between velocity and the direction of force. We know that \[\cos {{90}^{0}}=0\]
Therefore, the work done on the object in circular motion will be zero.

So, the correct answer is “Option C”.

Note:
Work done is circular motion is given as the product of the force and displacement in the direction of force. There is no work done in circular motion as the distance moved by the object is always perpendicular. Work is done on an object when the force I applied to the object to cause a displacement of the object.