Question

A body moving with a constant velocity on normal ground initially has an energy of 1000 J. If the final energy is 800 J, what is the work done and which force causes this work?

(a) 200 J, gravity

(b) -200 J, friction

(c) 200 J, friction

(d) -200 J, gravity

The question was posed to me in an interview.

My question is taken from Work-Energy Theorem topic in portion Work, Energy and Power of Physics – Class 11

Answer 1

Correct option is (b) -200 J, friction

To explain I would say: According to the work-energy theorem, the total change in energy is equal to the total work done. The change in energy is -200 J. Hence the work done is -200 J. Since it is mentioned that the body is moving on a normal ground, there is force is friction. Therefore, friction is what causes this work.