1. The problem statement, all variables and given/known data A 200g toy car is placed on a narrow 60 cm diameter track with wheel grooves that keep the car going in a circle. The 1 kg. track is free to turn on a frictionless, vertical axis. The spokes have negligible mass. After the car's switch is turned on, it soon reaches a steady speed of .75 m/s relative to the track. What then is the track's angular velocity in rpm? 2. Relevant equations L=I*angular velocity L=mrvsintheta Moment of Inertia for a hoop: I=MR^2 3. The attempt at a solution I found the angular momentum of the car and added it with the expression for the angular momentum of the track. The two combined should have a momentum of 0. (.200kg)(.30m)(.75m/s) + (1kg)(.30m)^2*angular velocity = 0 angular velocity = -.5 rad/s = -4.77 rpm According to my book the answer is 4 rpm and I was just wondering what I am doing wrong.