# Three masses on a pulley

1. Oct 26, 2008

### Maiia

1. The problem statement, all variables and given/known data
The pulley is massless and frictionless. A massless inextensible string is attached to these masses: 1kg, 3 kg, and 8kg. The acceleration of gravity is 9.8m/s^2. What is the tension T1 in the string between the block with mass 1kg and the block with mass 3kg (on the left hand side of the pulley)?

Picture of the problem:

My freebody diagrams for the problem

Fnet (1kg)= T1- Fg= ma
T1= Fg +ma

Fnet (3kg)= T2- T1- Fg= ma

Other than assuming that T1, T2 and T3 are all the same, I don't really know where to go from there...I would really appreciate it if someone could point me in the right direction.

2. Oct 26, 2008

### PhanthomJay

Your FBD's and application of Newton 2 are good thus far. As a hint, you should note that the tension in a string wrapped around a massless, frictionless pulley is the same on each side of the pulley , but don't assume that all tensions are the same! Now draw a FBD of the 8Kg block, which you have neglected to do. Then where do you go from there?

3. Oct 28, 2008

### Maiia

Oh, I see. So T2 and T3 are the same. That helps a lot. Thanks!