Originally Posted by member232

A 2 kg ball and an 8 kg ball are placed on the same spring at the same time. The spring is compressed and released. Which of the following is true about the maximum height reached by the balls?

A. The 2 kg ball will go four times as high.
B. The 2 kg ball will go twice as high.
C. The balls will reach equal maximum heights.
D. The 8 kg ball will go four times as high.

Answer: C

I guess my intuition is skewing things a bit for me. Would someone please explain the problem conceptually and/or with the math? The way I'm looking at it is:

Since the spring is the same, both balls start off with the same potential energy of 1/2kx^2
By conservation of energy 1/2 kx2 = mgh , so shouldn't the less massive ball reach a greater height?

I know there's something wrong in the way I'm looking at this... any clarification? Thanks in advance!