Question

Which of the following statement is incorrect?

• A. Work done in uniform circular motion is zero
• B. Work done in stretching a spring is positive
• C. Work done on a freely falling body is positive
• D. Work done depends on time taken

Hint:

In mechanics, work is defined as the product of force and displacement. Time is not directly involved in the definition of work, but it affects the power delivered during the work.

Answer 1

The Correct Option is D

- (A) Work done in uniform circular motion is zero: This statement is incorrect. In uniform circular motion, although the speed of the body is constant, the direction is changing. Therefore, there is a continuous change in the velocity vector, and centripetal force does work on the object. However, the net work done is zero because the centripetal force is perpendicular to the displacement at all points. - (B) Work done in stretching a spring is positive: This statement is correct. When a spring is stretched, work is done to overcome the restoring force exerted by the spring, and this work is stored as potential energy in the spring. - (C) Work done on a freely falling body is positive: This statement is correct. As the body falls, gravity does positive work on it, and the potential energy is converted into kinetic energy. - (D) Work done depends on time taken: This statement is incorrect. Work done only depends on the displacement and force applied, not on the time taken. The time taken affects the power, not the total work. Thus, the incorrect statement is (D) Work done depends on time taken.