# Tension of string on pulley?

1. Sep 26, 2008

### Ltcellis

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

Suppose the pulley is suspended by a cord C

Determine the tension in this cord after the masses are released and before one hits the ground. Ignore the mass of the pulley and cords.

Mass 1 : 1.2kg
Mass 2 : 3.2kg
Pulley and String mass is negligible

2. Relevant equations

T-m1g = -m1a
T-m2g = m2a
Tension of pulley = T(C) -mg - 2T = ma(?)

3. The attempt at a solution

So I solved for the tensions in both ropes. Since they're equal I got T=17N
For acceleraton I got 4.4545455m/s. I'm just not too sure on the equation on the Tension of Cord C. Would it be the equation I mentioned above? When I use that I get an answer around 96. Is that right?

2. Sep 26, 2008

### Staff: Mentor

No, it's much simpler than that. Since the pulley is massless, the sum of the forces on it must add to zero. (Note further that there is no mg term acting on the pulley.)

3. Sep 26, 2008

### Ltcellis

So it's just T(C) = 2T?

because I was thinking mg was referring to the total weight.

4. Sep 26, 2008

### Staff: Mentor

Yep, that's all it is.
You are analyzing the pulley, so mg can only refer to the weight of the pulley, which is zero.

5. Sep 26, 2008

### Ltcellis

Thanks a bunch