Name __________________________________
Period: 1 2 3 4 5 6 7
ENERGY CALCULATIONS
1. Does an object have energy when it is at rest? Explain your answer.
Yes. All objects have energy. It could have potential chemical energy, gravitation potential energy
or elastic potential energy which involves an object at rest.
2. A 250-kg rock falls off a cliff and comes to rest on the ground, which is 40 m below the cliff.
Where is the rock’s potential energy at maximum? at the top of the cliff
Where is the kinetic energy at maximum? right before it hits the ground
3. At what height is an object that weighs 490 N if its gravitational potential energy is 4900 N-m?
GPE = mgh
w = mg
GPE = wh
GPE = 4900 J
w = 490 N
h=?m
4900 J = 490 N x h
h = 10 m
4. A roller coaster car moving around a high turn has 100,000 J of GPE & 23,000 J of KE. What is its mechanical
energy?
ME = GPE + KE
ME = 100,000 J + 23,000 J
ME = 123,000 J
5. A girl on a motorbike passes by at a speed of 15m/sec. Her mass is 40 kg. What is her kinetic energy?
KE = ½mv2
KE = ½ x 40 kg x (15 m/s)2
KE = 4500 J
6. What speed does a 1-kg mass have when its kinetic energy is 1 N-m?
KE = ½mv2
KE = 1 J
m = 1 kg
v = ? m/s
1 J = ½ x 1 kg x v2
2 = 1 kg x v2
2 = v2
v = 1.41 m/s
7. How fast is a 6-kg sphere traveling if it has 55 N-m of energy?
KE = ½mv2
KE = 55 J
m = 6 kg
v = ? m/s
55 J = ½ x 6 kg x v2
110 = 6 kg x v2
18.3 = v2
v = 4.3 m/s
8. If your weight is 500 N, you are standing on a floor that is 20m above the ground, what is your GPE?
GPE = mgh
w = mg
GPE = wh
GPE = ?
w = 500 N
h = 20 m
GPE = 500 N x 20 m
GPE = 10,000 J
9. What is the kinetic energy of a 24-kilgram mass that is moving with a velocity of 2 m/s?
KE = ½mv2
KE = ? J
m = 24 kg
v = 2 m/s
KE = ½ x 24 kg x (2 m/s)2
KE = 48 J
10. A baseball that weighs 1.38 Newton’s is thrown so that it attains a velocity of 18 m/s. What is the kinetic
energy of the ball at that velocity?
w = mg
1.38 N = m x 9.8 m/s2
m = 0.14 kg
v = 18 m/s
KE = ½mv2
KE = ½ x 0.14 kg x (18 m/s)2
KE = 22.68 J
11. A rock with a weight of 156.8 Newtons falls 5 meters. What potential energy does it have just before it
falls?
GPE = mgh
w = mg
GPE = wh
GPE = 156.8 N x 5 m
GPE 784 J
12. A 10-kilogram mass is lifted to a height of 2 meters.
a. What is its weight?
w = mg
w = 10 kg x 9.8 m/s2
w = 98 kg
b. What is its potential energy at that height?
GPE = mgh
GPE = 10 kg x 9.8 m/s2 x 2 m
GPE = 196 J
13. A system has a total Mechanical energy of 350 J and KE of 220J. What is the PE?
ME = GPE + KE
ME = 350 J
KE = 220 J
GPE =? J
350 J = GPE + 220 J
GPE = 130 J
14. A car is traveling at 30 m/s with a KE of 900 J. What is its mass?
KE = ½mv2
KE = 900 J
m = ? kg
v = 30 m/s
900 J = ½ x m x (30 m/s)2
1800 = m x 900
m = 2 kg