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Homework Help: San Francisco YoYo

  1. Mar 25, 2014 #1
    1. The problem statement, all variables and given/known data
    A large yo-yo is released from a crane over San Francisco Bay. The 129 kg yo-yo consists of two uniform disks of radius 30 cm connected by an axle of radius 3.2 cm.
    (a) What is the magnitude of the acceleration of the yo-yo during its fall?
    (b) What is the magnitude of the acceleration of the yo-yo during its rise?
    (c) What is the tension in the cord on which it rolls?
    Hint: Use the equation for rolling down a ramp.

    2. Relevant equations
    a= -g/(1+I/mr^2) is the equation it is referring to
    For a disk, I=(mr^2)/2

    3. The attempt at a solution
    I'm stuck at finding I. I would apply the disk equation to each of the three disks in the yoyo. But it doesn't divide the three disks into their individual masses, so I don't know how to find I.
    Parts A and B should be the same, correct?
    And to find tension, F(total)=ma=F(gravity)-F(tension)=mg-F(tension), so F(tension)=mg-ma correct?

    Resolved myself....I don't really understand why this was correct but it was.
    I=((129 kg)(.3 m)^2)/2
    Last edited: Mar 25, 2014
  2. jcsd
  3. Mar 25, 2014 #2


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    Gold Member

    If you don't understand why, then it is not resolved!
    That's the right time to solve and learn.
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