Question

Each of the following statement describes a force acting. Which force is causing work to be done?

(a) the weight of a book at rest on a table
(b) the pull of a moving railway engine on its coaches
(b) the tension in an elastic band wrapped around a parcel
(d) the push of a person's feet when standing on the floor

Answer 1

We will justify all statements one by one as:
(a) The weight of a book at rest on a table cannot do any work as the book is at rest. So, the work done by this force is zero.
(b) The pulling force applied by the railway engine on its coaches is doing work, as the force applied by the engine results in the motion of the coaches.
(c) The tension force in an elastic band wrapped around a parcel cannot do any work, as there is no motion of the parcel because of the tension force of the rubber band.
(d) The push of a person’s feet on a floor when he is standing cannot do any work because there is no motion involved due to the applied force.

Therefore, the answer is -
(b) The pull of a moving railway engine on its coaches.