Posted by **Jamie** on Tuesday, January 2, 2007 at 4:27pm.

What is the spring constant of a spring that stores 25 J of elastic potential energy when compressed by 7.5 cm from its relaxed length?

I know that I should chnage 7.5 cm into .075 m. Is this equation correct? U(x)= 1/2kx^2. I should have gotten 89N/cm for the correct answer but it isn't working out.

U= 1/2 k x^2

k= 2U/x^2 = 2*25/.075^2=8900N/m^2 This does not convert to the answer you cited.

Or you can work it in cm..

U= 1/2 k x^2

2U/x^2 = 2*25/7.5^2 N/cm

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