Finding acceleration in the system

[1/2"]

Homework Statement

Find the acceleration of Blocks A and B in the given situation (Picture attached)

Homework Equations

~

The Attempt at a Solution

In this case I tried to do the free body diagram (i don't even know if its correct or not)

Block B has two tension forces acting upwards and its weight (5g) downwards
net force=5g-2T downwards
Block A has one tension force acting upwards and its weight (4g) downwards
net force=T-4g upwards

but what do i after that?Is the acceleration of A twice of B?
answer giver in my book is (2g)/7 downward,g/7 upwards(i think its most probably correct)
it would be really helpful if you could give me a clue.

 

[TSny]

Is the acceleration of A twice of B?]

Yes, hopefully you can come up with a good reason for that.

Try setting up Newton's 2nd law for each block. You'll have a system of equations that you can use to solve for the accelerations.

 

[voko]

You have two equations, and three unknowns: two accelerations and the force of tension. You need another equation to solve this. You can obtain this equation by comparing the velocities of the two blocks, and from that, their accelerations.