GPE = m g h = 80 x 10 x 30 = 24,000J or 24kJ
GPE = m g h = 1,200 x 10 x 8 = 96,000J or 96kJ
G.P.E. = 80 x 10 x 8848 = 7,078,400 or 7.08MJ
Potential and Kinetic Energy
There are two equations which you must be able to use
Gravitational Potential Energy G.P.E. = m g h
m = the mass of the object in kg
g = gravitational field strength in N/kg or m/s2 On Earth we take this as being approximately 10 m/s2
h = the change in height involved in m
Here are a few examples
| A bungee jumper of mass 80kg falls
30m. How much g.p.e. does he lose? GPE = m g h = 80 x 10 x 30 = 24,000J or 24kJ |
|
| A lift and its passengers have a
total mass of 1200kg. How much g.p.e. does it gain when it goes up 8m? GPE = m g h = 1,200 x 10 x 8 = 96,000J or 96kJ |
|
| How much g.p.e. would an 80kg person
gain when climbing Everest which is 8,848m? G.P.E. = 80 x 10 x 8848 = 7,078,400 or 7.08MJ |
|
Kinetic Energy K.E. = 1/2 m v2
m = the mass of the object in kg
v = the velocity of the object in m/s
Here are a few examples
| How much kinetic energy does a 170kg
bike and rider have at 30m/s? K.E. = 0.5 x 170 x (30 x 30) = 76,500J |
 |
| How much kinetic energy does a
700,000kg train travelling at 40m/s have? K.E. = 0.5 x 700,000 x (40 x 40) = 560,000,000 = 560MJ |
 |
| How much kinetic energy does a rifle
bullet of mass 70g travelling at 900m/s? K.E. = 0.5 x 0.07 x (900 x 900) = 28,350J = 28.4kJ |
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