**Conservation of Energy**

As a reminder; the conservation of energy states that the total amount of energy in a system is constant over time (i.e. if you put 5J in you get 5J out). A consequence of this is that energy can

**neither be created nor be destroyed**; and can only be

**transformed**from one state to another.

We
can write the principle of conservation of energy as a formula:

**Calculation**

The
Diagram below shows a man at the top of a building, calculate how much energy
he has at the start and hence show how much energy he has at the end.

**Energy at the top**GPE = mgh

GPE = 50 x 10 x 20

GPE = 10,000J

KE = 0J
(He isn’t currently moving)

Total
Energy = KE + GPE

Total Energy = 0 + 10,000

Total Energy at start = 10,000J

Total Energy = 0 + 10,000

Total Energy at start = 10,000J

**Energy at the bottom**GPE = 0J

Total
energy Start = Total energy End

Total
energy end = KE + GPE

10,000J = KE + 0J

10,000J = KE + 0J

KE = 10,000J

KE = ½ mv

10,000 = ½ x 50 x v

v = 20m/s

^{2}10,000 = ½ x 50 x v

^{2}v = 20m/s

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