# Help! Need help with an Atwood machine problem.

1. Oct 16, 2006

### Tyranicus

I was working on my physics homework and I came across a question that I couldn't find an example of in my notes.

I'm not sure which formulas I need to use and in which order to use them.

Here's the question:

Two objects with masses of 3.00 kg and 5.00 kg are connected
by a light string that passes over a light frictionless
pulley to form an Atwood machine, as in Figure
5.14a. Determine (a) the tension in the string, (b) the
acceleration of each object, and (c) the distance each
object will move in the first second of motion if they start
from rest.

Thanks for the help!

- Tyranicus

2. Oct 16, 2006

### BishopUser

try F = ma for the first two and maybe xf = xi + vit + 1/2at^2 for the third.

3. Oct 16, 2006

### Tyranicus

I know how to use F = ma but I don't know how to use the second formula.

Thanks very much

-Tyranicus

4. Oct 16, 2006

### BishopUser

You should be able to solve both A and B with just F = ma (by creating a system of equations). For the last part Xf = Xi + ViT + 1/2at^2. Xf is just the displacement that we want. Xi is initial position just set it to 0. Vi is initial velocity which is 0. So it's just D = 1/2at^2. You calculated the acceleration, and they give you the time they want.