Posted by Jordan on .
1. A certain playground merrygoround is essentially an 90kg iron disk 2.0 m in radius. Two children, each with a mass of 46 kg, are originally standing on opposite sides of the disk near its outer edge. The merrygoround is turning essentially without friction about a vertical axis once every 5 s. The children then clamber toward each other so that they are only 1.2 m from the center. What is its angular velocity now? (You do not need to specify its direction.)

Physics 
drwls,
Hint: Angular momentum is conserved.
The initial angular velocity is
w1 = (2*pi)/5 = 1.26 rad/s
Moment of inertia of the platform is
I = (1/2) M R^2 = 180 kg*m^2
There is additional angular momentum due to the children. Conservation of angular momentum requires that:
I*w1 + 2 m*5*2^2*w1 = I*w2 + 2*m*1^2*w2
m is each child's mass. Solve for w2