# Double Atwood Machine Question

1. Oct 4, 2011

### JoeBargo

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

http://i233.photobucket.com/albums/ee237/biggyjoe210/IMAG0175.jpg

1. Show that the Acceleration of Mass A is given by : (look at picture)

2. Relevant equations

F = ma

3. The attempt at a solution

So far all I have is a = g(mA-mB)/(mA+mB)

Im lost

2. Oct 5, 2011

### Spinnor

Did you draw any free-body diagrams?

3. Oct 5, 2011

### JoeBargo

Yeah all have tension going up and mg going down except the pulley which has tension up and tension down as well *** mg. The tension of string attaching a and b are the same and c and d are the same.

4. Oct 5, 2011

### Spinnor

Does the following look like I'm on the right track? Six equations in six unknowns.

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5. Oct 5, 2011

### JoeBargo

Yeah, I have that down. I solved for the smaller system(mA, mB, mD) for acceleration and tension. I'm guessing x is acceleration. If so thats exactly what I have. I can't get the algebra right or something when I solve for a1 and a2(the two separate accelerations of the strings). I keep getting close to the given formula but I'm messing up somewhere.

6. Oct 7, 2011

### cajunboy

hey do you go to tech??
m having problem with the same question...did you solved it??

7. Oct 7, 2011

### Raptorkiller

the trick is displace one body and see the motion of other bodies eg.if u displace the "Mc" body then the other two bodies(Ma and Mb) will as a whole go down but one of them will go up and other down relative to each other.then draw the free body diagram on each.NOTE: tension in the Mc body will be 2times that of ropes of other two.then write the equations involving T and g.gud luck

8. Oct 7, 2011

### nickw12

I'm also at Tech. I get some of it, but there are like 3 parts to the final equation that I'm missing. I'm still not exactly sure on how to do this.