An elevator is rising at constant speed. Consider the following statements: I. the upward cable force is constant
II. the kinetic energy of the elevator is constant
III. the gravitational potential energy of the Earth-elevator system is constant
IV. the acceleration of the elevator is zero
V. the mechanical energy of the Earth-elevator system is constant

Question

Quizplus · Accepted Answer

The elevator is moving at a constant speed, so the upward cable force (I) is constant and equal to the gravitational force. The kinetic energy (II) is constant because speed is constant. The acceleration (IV) is zero because the speed is constant. The gravitational potential energy (III) is not constant as the elevator rises. The mechanical energy (V) is not constant because potential energy changes.

An Elevator Is Rising at Constant Speed