college physics
posted by Anonymous .
A springloaded toy gun is used to shoot a ball of mass m= 1.50 kg straight up in the air. The spring has spring constant k = 667 N/m. If the spring is compressed a distance of 25.0 cm from its equilibrium position y=0 and then released, the ball reaches a maximum height h_max (measured from the equilibrium position of the spring). There is no air resistance, and the ball never touches the inside of the gun. Assume that all movement occurs in a straight line up and down along the y axis. Find v_m the muzzle velocity of the ball (i.e., the velocity of the ball at the spring's equilibrium position y=0). I just don't understand where to begin with this question

M*g* h_max = (1/2) M (v_m)^2
M cancels out.
Solve for the initial velocity, v_m .