I have a question about thse following system: block of mass M is attached to a spring is on an inclined plane.(adsbygoogle = window.adsbygoogle || []).push({});

Why do the force and energy analysis equations give different answers? The question is to find the maximum extension of the spring. Here is my thinking so far.

I know if you use energy convervation, you get 1/2*k*x^2 = M*g*sin(theta), so you get x = 2*M*g*sin(theta)/k.

However, why can I not just set the force along the incline equal to the spring force and solve for x that way? If I do that, I get a different answer:

k*x = M*g*sin(theta)

x = M*g*sin(theta)/k and this is different by a factor of 2.

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# Homework Help: Mass, spring, inclined plane

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