Energy of Harmonic Oscillators?

[erik-the-red]

Question:

Find the kinetic energy $$K$$ of the block at the moment labeled B. Express the answer in terms of $$k$$ and $$A$$.

Well, I know the potential energy at point B. That's $$U_B = (1/2)(k)(\frac{1}{2}A^2) = \frac{1}{8}kA^2$$.

How am I supposed to find the kinetic energy?

 

[quantumdude]

If you can answer the following questions in order, then I think you'll arrive at the solution:

1.) What is the potential energy at moment A?
2.) What is the kinetic energy at moment A?
3.) What is the total energy at moment A?
4.) What therefore must be the total energy at any moment?
5.) What is the potential energy at moment B? (You already got this one).
6.) Using your answers to questions 4 and 5, what is the kinetic energy at moment B?

Give that a shot and see if you can't solve the problem.

 

[erik-the-red]

Thanks. The answer was right in front of me :D