Homework Help: Find tension between blocks 2 & 3

1. Feb 29, 2012

Rey4312

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

There are three blocks connected by strings as shown in the figure. Each block has the mass as following mass,
m1=0.8kg
m2=2.2kg
m3=1.7kg
Assuming there is no friction,

2. Relevant equations

F=MA

3. The attempt at a solution

In my FBD of the hanging box
$\uparrow$ <--- Tension
[]
$\downarrow$ <--- W=mg

^^ in y direction: T-W=0
T=W

The FBD of the box on the table
$\uparrow$ <---Normal Force
[] $\rightarrow$ <--- Tension
$\downarrow$ <--- W=mg

^^ x direction: t=0
y direction: Fn-W=O

But im completely confused on how to find the tension of the boxes

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2. Feb 29, 2012

tiny-tim

Welcome to PF!

Hi Rey4312! Welcome to PF!

Call the tensions "T1" and "T2", and the acceleration "a" (it'll be the same for all three boxes, won't it? )

Then do F = ma three times, once for each box, and solve …

what do you get?

3. Feb 29, 2012

Rey4312

But if i do that the acceleration = 0 and so it makes all the forces 0... right??

or am i missing something and it should be gravity?

4. Feb 29, 2012

tiny-tim

Yes, you need to include W (=mg) for the hanging box.

5. Feb 29, 2012

Rey4312

W for the hanging box is 16.66

and W for box 2(m2) is 21.56....

Where do i go from there, because that doesn't give me acceleration....

6. Feb 29, 2012

Rey4312

i figured it out... i ended up having to do m2a+m1a