Question

A car is being lifted by a crane so that it moves upwards at a constant speed.

(a) Which force is doing negative work on the car as it is being lifted? a. The force of the rope acting on the car. b. The force of gravity on the car due to the Earth. c. The force of the car acting on the rope. d. There is no work being done because the kinetic energy of the car is constant.

Answer 1

b

Step-by-step explanation:

(b) The force of gravity on the car due to the Earth is doing negative work on the car as it is being lifted because the force of gravity is in the opposite direction to the displacement of the car. Negative work is done when the force and the displacement are in opposite directions. In this case, the force of gravity is acting downwards while the car is moving upwards. The force of the rope acting on the car is doing positive work because it is in the direction of motion of the car.