1. The problem statement, all variables and given/known data A piece of putty of mass m = 0.75 kg and velocity v = 2.5 m/s moves on a horizontal frictionless surface. It collides with and sticks to a rod of mass M = 2 kg and length L = 0.9 m which pivots about a fixed vertical axis at the opposite end of the rod as shown. What fraction of the initial kinetic energy of the putty is lost in this collision? 2. Relevant equations KE = 1/2mv^2 KE = 1/2Iw^2 L=mvr L=Iw I=mL^2/3 I=mr^2 r=L (I'm using the pivot as the point of origin) 3. The attempt at a solution Based on the wording, it's an inelastic collision, and the putty sticks to the rod. So, momentum is conserved: mvL = (mL^2/3+mL^2)w Using numbers, I found that w = 1.176 rad/s The initial KE is 1/2mv^2= 2.34 The final KE is 1/2Iw^2= 0.79 KElost/KEi=(KEi-KEf)/KEi = 0.66 but the answer is wrong.