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Q & A: kinetic plus potential energy

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Most recent answer: 07/30/2013
Q:
Can KE (1/2MV2) + PE (MGH) = the total amount of energy in a object? Also, is this another way to work out the famous equation E=MC2?
- Jess (age 13)
Sydney, NSW, Australia
A:

That expression can work for the total energy in some limited circumstances.

1. Nothing major (e.g. nuclear reactions) happens to change M, so you can ignore the rest energy.

2. There's a uniform gravitational field g so you can write the gravitational potential energy in that simple form.

3. The speed v is much less than c and you don't consider any distances with gh comparable to c2, so you can ignore relativistic effects.

E=mc2 is not especially hard to work out, but these equations definitely are not the path to get there.

Mike W.


(published on 07/30/2013)

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