When a block slides a certain distance down an incline the work done by gravity is 300 J. What is the work done by gravity if this block slides the same distance up the incline?

Question

a) 300 J
b) zero
c) -300 J
d) It cannot be determined without knowing the distance the block travels.
e) It cannot be determined without knowing the coefficient of friction

I think the answer is b) since gravity can only act downwards.

Nonsense. Gravity makes my car go down hills, and resists going up, and in neither case we travel vertically.

What does friction do when something slides down an incline?

So would that make the answer c) -300 J? Work= Fd and so the force is the same but the direction is different.

Answer 1

Yes, that is correct. The answer is c) -300 J. The force of gravity is the same, but the direction of motion is opposite, so the work done by gravity is negative when the block slides up the incline.