A 50.0 kg skier is at the top of a slope. At the initial point A, the skier is 10.0 m vertically above B?

Question

A 50.0 kg skier is at the top of a slope. At the initial point A, the skier is 10.0 m vertically above the final point B.

(a) Set the zero level for gravitational potential energy at B, and find the gravitational potential energy of the skier at A and B. Then find the difference in potential energy between these two points.

(b) Repeat this problem with the zero level at point A.

(c) Repeat this problem with the zero level midway down the slope, at a height of 5.0 m.

How do you do parts b and c
what does it mean by

zero level at point A and

with the zero level midway down the slope, at a height of 5.0 m.

OK i got the other questions but i don't get the (b)
What do i do when it says:
Repeat this problem with the zero level at point A

Answer 1

ΔP.E. = Δmgh
with m and g constant,
ΔP.E. = mgΔh

(a)
E(A) = 50*10*9.8 = 4900 J
E(B) = 0
ΔE = 4900 J

(b) and (c) have similar solutions.