The left side of the figure shows a light (`massless') spring of length 0.280 m in its relaxed position. It is compressed to 67.0 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 1.10 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.