Where Does the Kinetic Energy Equation KE = mgR(1-cos theta) Originate?

[Nash77]

For a particular homework problem, we needed to find an angle theta.

This equation was used: h = L(1 - cos theta) to solve for theta.
I guess that came from the Kinetic Energy equation KE = mgR(1-cos theta),
but where does that kinetic energy equation come from?

Is it just an equation to know, or was I supposed to have derived this from something?

Thanks,
Nash

 

[SammyS]

Without seeing the particular homework problem, it's impossible to help you.