# Homework Help: Playground/merrygo round problem. Rotational kinematics

1. Oct 2, 2016

### iknowsigularity

1. The problem statement, all variables and given/known data
In a playground there is a small merry-go-round of radius 1.20 m and mass 220 kg. The radius of gyration is 91.0 cm. A child of mass 44.0 kg runs at a speed of 3.00 m/s tangent to the rim of the merry-go-round when it is at rest and then jumps on. Neglect friction between the bearings and the shaft of the merry-go-round and find the angular speed of the merry-go-round and child.

I have no idea how to go about starting this, so I'm not looking for an answer just perhaps what equation I should be using. thanks for any help!

2. Oct 2, 2016

### Staff: Mentor

You need to state what you know and what the results are of your researching the problem. You can't have absolutely no idea if this is part of a course assignment. What equations pertain to the type of motion involved? What type of interaction is occurring?

3. Oct 2, 2016

### iknowsigularity

I assume possibly the conservation of angular momentum? and maybe you take the tangential speed of the child and transform it to angular speed?

4. Oct 2, 2016

### Staff: Mentor

Okay, start there. Clearly there's a collision taking place (what type, elastic or inelastic?). What information will you need to know to handle a collision problem? (Think of a linear collision problem and what you'd want to know for that scenario. What are the angular motion analogs to those things?)

5. Oct 2, 2016

### iknowsigularity

so would perhaps the conservation of kinetic energy formula work?
or actually its the conservation of angular momentum so (moment of inertia)(angular speed) intial = (moment of inertia)(angular speed) final?

6. Oct 2, 2016

Yes.