Question

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

Which force is doing negative work on the car as its being lifted?

a) The force of the rope acting on the car
b) There is no work being done because the kinetic energy of the car is constant
c) The force of gravity on the car due to the Earth
d) The force of the car acting on the rope

Part 2: Which force is doing positive work on the car as it's being lifted?
a) The force of the Earth acting on the car
b) There is no work being done because the kinetic energy of the car is constant
c) The force of the rope acting on the car
d) The force of the car acting on the rope

Answer 1

Step-by-step explanation:

Work done is defined as the product of force and the displacement in the direction of force.

W = F x d x Cos θ

Where, θ be the angle between force and the displacement.

The force of gravity acts downwards and the displacement is in upward, so the angle is 180. cos 180 = -1 , so the work done by the force of gravity is negative.

The force of rope acting in upwards direction and displacement also in upwards direction.

So, the work done is positive