This is not so much a homework problem as it is a question: How do I know whether an object has kinetic energy or potential energy? I know for potential energy you make a point that is PE(grav) = 0, and then if the object reaches a height you make the other PE = mgh. So in (KE_2 - KE_1) - (PE_2 - PE_1) - (S_2 - S_1) = W_other where KE = kinetic en. PE = potential en S = spring en W = other forces acting... If no other forces are acting on the object W_other = 0; and there is no spring = 0 - 0 Then you get (KE_2 - KE_1) = - PE_2 + PE_1 And then if you make a point that is PE_1 = 0 KE_2 - KE_1 = -PE_2 Then what about KE ? Does that make KE_2 = 0? I have no idea, please help me! I need an answer in 9 hours!