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BlameTruth

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## Homework Statement

Two identical cylinders of mass M and radius R are mounted on frictionless axles as pictured above. Around each cylinder a massless thread is wound. The hanging thread on the left is wound around a third identical cylinder. A box of mass M is attached to the hanging thread on the right. Both systems are released from rest. After the cylinder has fallen a distance of 8.0 meters, it will have a translational speed of ____ m/s. Use 10 for acceleration due to gravity.

On a side note, the system on the right was used for a previous problem.. hence its uselessness.

## Homework Equations

Not sure which of these are relevant:

[tex]\tau = r x \alpha[/tex]

[tex]\tau = I \alpha[/tex]

[tex]KE_t = \frac{1}{2}mv^2[/tex]

[tex]KE_r = \frac{1}{2}I\omega ^2[/tex]

Gravitational potential energy = [tex]mgh[/tex]

## The Attempt at a Solution

I tried an approach using Newton's second law and summing the forces that act on the cylinder that is falling.. but attempting that got me down to 1=1 (yay). My friend claims that a conservation of energy approach is the way to go, but I really don't know where to start. If someone could push me in the right direction, that'd be wonderful. This is, apparently, the hardest problem that my AP Physics class will encounter all year (according to the instructor).