You're designing a toy rocket to be launched by a spring. The launching apparatus has room for a spring that can be compressed 14 cm, and the rocket's mass is 65 g. If the rocket is to reach 35 m altitude, what should be the spring constant? [tex]U_o = 1/2*kx^2[/tex] [tex]K_o = 0[/tex] well work is being stored so K = 0 and U has the spring energy right? [tex]U_f = mgh[/tex] [tex]K_f = 0[/tex] U_f = mgh because of the gravitational potention energy right? and K_f = 0 because it's at rest right when it reaches 35m? I'm not sure if K_f = 0 or not because i dont really know if the rocket is at it's max height when it reaches 35m. well, setting them equal to each other... [tex]1/2*kx^2 = mgh[/tex] and solving for k, i get 3.1 but the book gets 2.3 kN/M. what am i doing wrong?