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Energy Transfer

Gravitational Potential Energy to Kinetic Energy.

When an object with GPE starts to fall, its GPE is transferred into KE.
The further the object falls, the less GPE it has and the more KE it has.
When the object hits the ground, all of its GPE has been transferred into KE.

Some processes transfer GPE to KE to GPE to KE and so on.
Examples are a bouncing ball, a pendulum and a comet.

If we look at the example of the 75 kg rock 4·0 metres above the ground,
we can calculate that it has 3000J of GPE.
Using the equation for KE,
we can calculate how fast it is travelling when it hits the ground.
All of the rock's GPE has become KE,
so the rock has 3000J of KE when it hits the ground.

KE  =  ½mv2

3000 = 0·5 x 75 x v2

v2 = 3000 ÷ (0·5 x 75)
= 80

v = 80
              = 8·94 m/s.

Since we now know how fast the rock was travelling,
we can calculate how long it took to fall the 4·0 metres.
Try it using the equation for acceleration.
a = 10 m/s2 (for gravity), v = 8·94 m/s, u = 0
(the answer is t = 0·894 seconds).

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Copyright © 2008 Dr. Colin France. All Rights Reserved.