Merry-go-round at rest, inertia, kid running on it problem.

[1barcafan]

Homework Statement

a 45kg child runs with a speed of 3.50m/s tangential to the rim of a stationary merry-go-round that has a momentum of inertia of 555 kg m^2, and a radius of 2.45m. when the child jumps off, the entire system begins to rotate. what is the angular speed of the system?

Homework Equations

The Attempt at a Solution

i found the circumference of the merry-go-round. assuming initial displacement is 0, final is 15.39 (circumfrence), initial velocity is 3.50m/s, and final velocity is 0, i found time to be 8.79s and acceleration to be -.40 m/s^2. using that acceleration and the mass of the child i found force, then using that force and distance i found torque. (i wasn't even taught torque, i just watched a youtube video on it and it seemed appropriate to incorporate it into this problem). once i did all of this, i just got stuck, I've never had a problem that asked for angular speed before so this is just something completely foreign.

 

[tiny-tim]

Hi 1barcafan!

a 45kg child runs with a speed of 3.50m/s tangential to the rim of a stationary merry-go-round that has a momentum of inertia of 555 kg m^2, and a radius of 2.45m. when the child jumps off, the entire system begins to rotate. what is the angular speed of the system?

I don't understand the question.

Are you sure it doesn't say that the when the child jumps onto the merry-go-round, the entire system (ie merry-go-round plus child) begins to rotate?

Anyway, this has nothing to do with acceleration (or torque ).

This is a collision, so use conservation of angular momentum.