1. Gravitational Potential & Kinetic Energy
Mechanical Energy
Gravitational Potential & Kinetic Energy

2. Gravitational Potential Energy:
Note: Same formula as W = Fd
Stored energy of a raised object
Gravitational Potential Energy (J)
Mass of object (kg)
Gravity (N/kg)

3. Ex #1
How much potential energy does a 61.2kg boy have if he is sitting on his bed, 0.5m above the floor?
m = 61.2 kg
g = 9.8 N/kg
∆h = 0.5 m

4. Ex #2
A 0.04kg rubber ball drops from a height of 5m to the ground & bounces back to a height of 3m.
a) How much potential energy does the ball lose on the trip down?
m = 0.04 kg
g = 9.8 N/kg
∆h = 5 m
b) How much potential energy does the ball regain on the trip back up?

5. Speed of the object (m/s)
Kinetic Energy:
Energy of an object due to its motion
Result of work having been done to the object
Kinetic Energy (J)
Speed of the object (m/s)
Mass of object (kg)

6. Ex #3
What is the kinetic energy of a 6kg curling stone sliding at 4m/s?
m = 6 kg
v = 4m/s

7. Ex #4
What is the speed of a 5.44kg shotput if its kinetic energy is 68J?
m = 5.44 kg
Ek = 68J

8. Ex #5
A 0.5kg rubber ball is thrown into the air. At a height of 20m above the ground, it is traveling at 15m/s. What is the ball’s Ek & Eg?
So ball has
154.25J of
total energy
m = 0.5 kg
m = 0.5 kg
g = 9.8 N/kg
v = 15m/s
h = 20 m

9. BUT….total energy (ET) still the same throughout
Eg = high
Ek = zero
Eg = high
Eg = lower
Ek = low
Ek = higher
Eg = higher
Ek = lower
Eg = zero
Ek = high

10. Total Mechanical Energy (ET):
Energy can be transferred or transformed, never lost  Law of Conservation of Energy
*If friction negligible
If friction is not negligible then….