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?
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.
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.
Yes, you are correct. The work done by gravity when the block slides down the incline is 300 J in the downward direction. When the block slides the same distance up the incline, the work done by gravity would be in the opposite direction, which is upward. Therefore, the work done by gravity would be -300 J, as stated in option c).
To determine the work done by gravity when the block slides the same distance up the incline, we need to consider the forces acting on the block in both scenarios.
First, let's understand the role of friction when something slides down an incline. Friction acts opposite to the direction of motion, slowing down the block's movement. In this case, the work done by friction is negative because it opposes the motion of the block.
When the block slides down the incline, gravity and friction are both acting on it. The work done by gravity is positive because it acts in the same direction as the displacement of the block. The work done by friction is negative because it acts in the opposite direction of the displacement.
Now, when the block slides the same distance up the incline, the direction of the displacement changes. In this case, the work done by gravity would be negative because it acts in the opposite direction of the displacement.
So, the correct answer is c) -300 J, as the work done by gravity is negative when the block slides up the incline.