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**1. Homework Statement**

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. Homework 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.