# Homework Help: Urgent: Atwood Machine Energy and Work

1. Oct 21, 2012

### kchurchi

1. The problem statement, all variables and given/known data

An atwood machince has a m1 = 4.92-kg block resting on a frictionless horizontal ledge. This block is attached to a string that passes over a pulley, and the other end of the string is attached to a hanging m2 = 2.46-kg block.

The pulley is a uniform disk of radius 8.06 cm and mass 0.615 kg. Calculate the speed of the m2 = 2.46-kg block after it is released from rest and falls a distance of 2.67 m.

2. Relevant equations

Work = ∫F dot ds

ΔE = ΔKE(translation) = 1/2*m2*vf^2 - 1/2*m2*vi^2

3. The attempt at a solution
At first I assumed only the weight force was doing work on mass 2 but I got the wrong answer. Then I thought perhaps tension was also doing work on mass 2. In order to find the tension force, I need to find the torques acting on the pulley and the sum of the forces acting on mass 1. I can do all of this, however, I would like to know if there is an easier, less complex way to do this problem.
Thanks!

2. Oct 21, 2012

### Staff: Mentor

You can use energy conservation, so you don't have to care about the details of the acceleration. Don't forget the pulley disk.

3. Oct 21, 2012

Thanks mfb!