Answer:
ΔU = -17640 J
Step-by-step explanation:
use the formula ΔU = mgΔh for the change in potential energy
m = 60 kg
g = 9.8 m/s^2
Δh = 60 - 90 = -30 m
ΔU = mgΔh
ΔU = 60 * 9.8 * -30
ΔU = -17640 J
there was a decrease of 17640 joules in potential energy