The Gravitational PE (U) depends on three things: the object’s mass (m), its height (h), and gravitational acceleration (g), which is 9.81 m/s^2 on Earth’s surface.
so U = mgh = 9.81mh on earth
mass of the car = 50.0 grams = 0.05kg
height, h:
Hill 1 = 90.0 cm = 0.9m,
Hill 2 = 65.0 cm = 0.65m,
Hill 3 = 20.0 cm = 0.2m
substitute into eqn U = mgh
U @ top of Hill 1 = 0.05*9.81*0.9 = 0.4415J
U @ top of Hill 2 = 0.05*9.81*0.65 = 0.3188J
U @ top of Hill 3 = 0.05*9.81*0.2 = 0.0981J
difference in Gravitational Potential Energy from the top of Hill 1 to the top of Hill 3 = 0.4415 - 0.0981
= 0.3434J where J is the unit for energy, Joules
The question has provided the most important equation:
The Gravitational PE (U) = the object’s mass (m) x its height (h) x gravitational acceleration (g)
Only trick here is the unit for each variable: PE (U) is in J which is kg-m/s^2-m; mass (m) is kg; gravity (g) is m/s^2 and height (h) is m.
With the conversion factors of gram=1/1000kg and cm=1/100m, U can be calculated as follows:
Hill 1=(50/1000)x(90/100)x9.81=0.44J
Hill 2=(50/1000)x(65/100)x9.81=0.32J
Hill 3=(50/1000)x(20/100)x9.81=0.098J
The difference in PE from Hill 1 to Hill 3
=0.44-0.098
=0.342J
