The elastic potential energy stored in a spring stretched by extension x with spring constant k is
- A. kx
- B. half kx squared
- C. kx squared
- D. half kx
Explanation
The force rises linearly from zero to kx, so the average force is half of kx and the work done is half k x squared, which is also the area under the force extension graph. This is why doubling the extension quadruples the stored energy. The formula holds only while Hooke's law applies, that is below the elastic limit.
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