I have been working on this problem for an hour and can't seem to figure it out. I know there must be something fundamental that I must be doing wrong. Can someone give me a pointer? A platform of mass 0.8 kg is supported on four springs. A chunk of modeling clay of mass 0.6 kg is held above the table and dropped so that it hits the table with a speed of v = 0.9 m/s. The clay sticks to the table so that the the table and clay oscillate up and down together. Finally, the table comes to rest 6 cm below its original position. With what amplitude does the platform oscillate immediately after the collison? In the first part of the problem I found that k=98.1 N/m. So, initially, the E is entirely Kinetic (KE = .5mv^2) for the intial velocity of 0.9 m/s and the mass of the clay (0.6 kg). This means that intial E = initial KE = 0.243. Now, I don't know if the final E is kinetic and potential, or just potential? if I say it is kinetic too, then how do I find V right after the collision? I tried the equation v= (mvi+Mvi)/(m+M) and calculated (0.6*0.9+0)/(0.6+0.8)=0.3857 m/s. If I use this velocity for final KE, and solve for A in the final PE (PE=.5kA^2), I get the wrong answer (A=0.053m) If I don't incorporate final KE and simply say that final E = final PE, then I get A=0.0703m, which is wrong too. What am I doing wrong? Which one do I use? And why is it that both give me the wrong answer?