1. The problem statement, all variables and given/known data A 5-gram bullet is shot horizontally at a 2-kg wooden block resting against a relaxed 100 N/m spring (the other end of the spring is fixed against a wall, the spring and the block sitting on a horizontal, frictionless table). It is observed that the bullet bounces back at 50 m/s and that the spring shows a maximal compression of 5-cm. A) What was the initial speed of the bullet? B) What fraction of the initial kinetic energy of the bullet was lost during the collision? m of bullet = .005 kg M of wooden block = 2 kg Vfinal of bullet = 50 m/s Max compression (x) = 5-cm = .05 m 2. Relevant equations Looks like elastic collision so .. total momentum is conserved as well as kinetic energy. KE = (1/2)m*v^2 EPE = (1/2)k*x^2 3. The attempt at a solution When spring is completely compressed: KEinitial(bullet) = PE(spring) + KEfinal(bullet) (1/2).005*v^2 = (1/2)*100*.05^2 + (1/2).005*50^2 Would this be right? It seems too simple to me .. Any help is appreciated.