# San Francisco YoYo

**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?

**Update:**

Resolved myself….I don’t really understand why this was correct but it was.

I=((129 kg)(.3 m)^2)/2

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