Question

An elevator supported by a single cable descends a shaft at a constant speed. The only forces acting on the elevator are the tension in the cable and the gravitational force. Which one of the following statements is true? A) The magnitude of the work done by the tension force is larger than that done by the gravitational force. B) The magnitude of the work done by the gravitational force is larger than that done by the tension force. C) The work done by the tension force is zero joules. D) The work done by the gravitational force is zero joules. E) The net work done by the two forces is zero joules.

Answer 1

Answer:

E) The net work done by the two forces is zero joules.

Explanation:

As the elevator is moving at a constant speed, it is the same as being stationary. The tension in the cable perfectly balances the gravitational force. Work done by gravity = mgh

Work done by the tension = -Th

where, T = tension force. The negative sign comes as the direction of T is opposite to the direction of g. As the elevator moves at a constant speed, the magnitude of the two forces must be equal. Therefore, the total work done,

W = (mg - T)h = 0