# Homework Help: TTU Dynamics: Find normal/angular acceleration of a point on a merry go round

1. Nov 4, 2012

### Green Lantern

1. The problem statement, all variables and given/known data

A boy mass mb and a girl mg are riding on a frictionless merry go round mr that has mass moment of inertia I = 1/2(mr)R^2. The boy runs back and forth from center to edge and completes a circuit in 2 seconds. If the initial speed is ωo, what is the acceleration the girl experiences on the outer edge R?

2. Relevant equations

I = 1/2(m)r^2
F = ma
M = dH/dt
M = F cross r

3. The attempt at a solution

I have as my diagram a circle that I assume spins clockwise. The plane of the circle is the y-z plane, so I have all weights pointing in the -i direction. There is 1 degree of freedom. I can apply F = ma right away and get:

F = -(mr + mb + mg)gi

I am unsure of how to go about tackling the rest of the problem. I have to assume the merry go round is a circular plate. I assume the girl and boy can be treated as point masses, since no mass moment of inertia is given for them. My knowledge of angular dynamics is rusty. What am I not seeing here?