# Help with 3 objects/masses connected by string over frictionless pulley?

1. Oct 4, 2009

### miamirulz29

1. The problem statement, all variables and given/known data
Three masses connected by light strings are shown in the figure below (I will try my best in describing the figure):
There is light, frictionless pulley with two masses, M2 and M3, on the left and one mass, M1, on the right. They are all connected by light strings. Given m1 = 10 kg, m2 = 7.48 kg, m3 = 8.01 kg, and g = 9.8 m/s2. The acceleration of gravity is 9.8 m/s2 . Find the downward acceleration of m2 mass. answer in units of m/s^2

2. Relevant equations
SigmaF= ma
mg=fg

3. The attempt at a solution

I drew three separate free body diagrams for each of the masses.
For M1:
Ft-MG=MA
Ft-98=10a

For M2:
MG-Ft=MA
7.48(9.8)-Ft=7.48a
73.304-Ft=7.48a

So I combined the two equations and got -1.413 m/s^2. I though because it is downward, I didn't need the negative, so I put in UT, 1.413, it was wrong, I also put -1.413, it was also wrong. Then I tried using M3 and combined the acceleration of M3 and M2, which was 8.387, which is also wrong. Then I read on another thread that you can use the equation:
A= [(M1-M2)/(M1+M2)] * G. I got 1.413. I honestly don't know what to do at this point, can somebody please help me. Thanks in advance.

2. Oct 4, 2009

3. Oct 4, 2009

### shootingrubbe

If you could post the diagram that would help a lot so we would know where to start...

4. Oct 4, 2009

### miamirulz29

Diagram posted. It is on the last page, number 018 (part 1of 3).

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5. Oct 4, 2009

### miamirulz29

Please can anybody help? I even posted the diagram.

6. Oct 4, 2009

### miamirulz29

Nevermind, figured it out.