1. The problem statement, all variables and given/known data The left side of the figure shows a light (`massless') spring of length 0.330 m in its relaxed position. It is compressed to 71.0 percent of its relaxed length, and a mass M= 0.210 kg is placed on top and released from rest (shown on the right). The mass then travels vertically and it takes 1.50 s for the mass to reach the top of its trajectory. Calculate the spring constant, in N/m. (Use g=9.81 m/s2). Assume that the time required for the spring to reach its full extension is negligible. 2. Relevant equations F=-kx 3. The attempt at a solution I'm not too sure about how I consider the time it takes for the mass to go back up. I know that the energy while the mass is on the spring is mg (downwards) and -kx upwards. Then when the ball goes back up - its KE + mgh is equal to mg-kx? thanks!