# Static equilibrium and tension problem

1. Dec 15, 2007

### Vanessa23

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

Four blocks with masses 2kg, 4kg, 6kg, 3kg are held together with ropes with tensions Tx, Ty, Tz. There is a force of 20N pointing to the right and 50N to the left. Find Tz.

2. Relevant equations

3. The attempt at a solution

This is like the static equilibrium problems, yet everything is moving. How do I find Tz?

2. Dec 15, 2007

### Staff: Mentor

F=ma on each block. Since the ropes are not stretching a is the same for all blocks.

3. Dec 15, 2007

### Vanessa23

So, since a is the same for all the blocks would I say:

50N-20N=15kg*a
a=2m/s

then F on box D would be Tz-48N=3kg*2m/s
Tz=54N

I feel hesitant not including the other masses and tensions...

4. Dec 15, 2007

### Staff: Mentor

If you want to work out all of the other tensions for each mass you certainly can, but all it will do is make you feel more confident :)

EDIT:
Where did the 48N come from, shouldn't that be either 20N or 50N depending on how the blocks are arranged?

Last edited: Dec 15, 2007
5. Dec 17, 2007

### Vanessa23

Sorry, I meant
Tz-20N=3kg*2m/s
Tz=26N

but why does it not matter what all of the other tensions, masses, and forces are? Why doesn't the calculation for Tz include the fact that there is a 50N force in the other direction as well as other blocks and other ropes?

6. Dec 17, 2007

### rl.bhat

While calculating the acceleration of the whole system you have taken into account all the forces and masses. They have named the tensions as Tx,Ty and Tz to make sure that which tension you have to calculate, proveded you arrange the blocks in same order as given in the problem.

7. Dec 17, 2007

### Vanessa23

So, then what would happen if the question asked for the middle tension?

8. Dec 17, 2007

### rl.bhat

Wright the expression for Ty - Tz