Homework Help: A person jumps on a merry go round, how much does the merry weigh?

1. May 4, 2010

smhippe

1. The problem statement, all variables and given/known data
A person with a mass of 52 kg runs with a speed of 6.8 m/s jumps onto the outer rim
of a merry-go-round. The merry-go-round has a radius of 1.5 m and can be modeled as a
large disk. The merry-go-round was initially at rest before the person jumped onto it and
rotates at 1.3 rad/s immediately after the person jumps on. What is the mass (in kg) of
the merry-go-round?

2. Relevant equations

Mm=Mass of merry go round
Mp=mass of person
Vp= velocity of person
w=angular velocity

3. The attempt at a solution
I just need someone to make sure I set this up right. I solved this using momentum. The initial momentum was Mp*Vp*r
The final momentum is 1/2*Mm*R^2*w+Mp*R^2*w
Solving I got 52*6.8*1.5=1/2*Mm*(1.5^2)*1.3+52*(1.5^2)*1.3

So does it look right to anyone?

2. May 4, 2010

Staff: Mentor

Looks right to me. (Assuming the person was moving tangent to edge of the merry go round when he jumped on.)