There is a rocket on a stage connected a spring with the spring constant k(N/m). The weights of the rocket and the stage are m(kg) and M(kg), respectively. The length of the spring without the stage and rocket or free is h0(m) and it becomes shrunk to h(m) on putting the rocket on it. Now, the rocket is launched with the initial velocity of v0. In this situation, answer the below questions, where the gravitational acceleration is g (m/s2), and the weight of the spring and resistance force due to air are negligible.

c) By launching, the spring is more shrunk. What is the energy stored in the spring when it is most shrunk?
d) What is the length of the spring at (c) situation.