Question

Suppose a 4,000-kg elephant is hoisted 20 m above Earth’s surface. Use a calculator and follow the steps below to find the elephant’s gravitational potential energy.
Step 1:
Calculate the elephant’s weight
(w = mg)

Step 2:
What is the GPE of the elephant?
(GPE = w * h)

Answer 1

GPE = 78,380 J
w = 39,240 N

First list what you know. You know the elephants mass and it’s height. You also know gravity on Earth. I will use g = 9.81.
m = 4,000 kg
h = 20 m
g = 9.81 m/s^2

You need to find the elephants weight. Weight = mass x gravity
w = mg
w = (4000 kg)(9.81 m/s^2)
w = 39,240 N (N = newtons)

Now, knowing the elephants weight, you can calculate its GPE.
Gravitational Potential Energy = weight x height

GPE = wh
GPE = (39,240N)(20m)
GPE = 78,380 J (J = joules)