The correct equation that shows the conservation of mechanical energy for the system of the marble and the compressed spring is:
\[ \frac{1}{2} mv^2 = \frac{1}{2} k x^2 \]
This equation indicates that the kinetic energy \(\frac{1}{2} mv^2\) of the marble when the spring is released is equal to the potential energy stored in the spring \(\frac{1}{2} k x^2\) when it is fully compressed. Therefore, the correct response is:
12mv2=12kx2 1 half m v squared is equal to 1 half k x squared