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

  1. May 4, 2010 #1
    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
    R=radius of merry go round
    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. jcsd
  3. May 4, 2010 #2

    Doc Al

    User Avatar

    Staff: Mentor

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