Calculating Tension - Homework Statement & Solution

[FOX2PRO]

Homework Statement

http://img293.imageshack.us/img293/1212/47236686fi5.png

I have to find the acceleration (magnitude and direction)
Tension in T1, and T2

Homework Equations

a = F/m P = F/A Fg = mg

The Attempt at a Solution

Well, i figured out the acceleration, by finding the difference in Fg between the two sides, and dividing that by the mass. I get .75m/s^2. Using that, I can get that the net force is 7kgx.75m/s^2 = 5.25N

I don't know how to get from there to the tension, mostly b/c the forces are changed by gravity, and tension is affected by gravity.

 

[alphysicist]

Hi FOX2PRO,

The Attempt at a Solution

Well, i figured out the acceleration, by finding the difference in Fg between the two sides, and dividing that by the mass. I get .75m/s^2. Using that, I can get that the net force is 7kgx.75m/s^2 = 5.25N

I don't know how to get from there to the tension, mostly b/c the forces are changed by gravity, and tension is affected by gravity.

Draw a free body diagram for the 4kg mass. What does that give?

 

[FOX2PRO]

Well, there's the force of gravity 4kg(9.8), and the net force, 5.25N
So, they are at opposite ends, so the tension would be 36.2N?

 

[alphysicist]

Well, there's the force of gravity 4kg(9.8), and the net force, 5.25N
So, they are at opposite ends, so the tension would be 36.2N?

Gravity is pulling down on the 4kg block, but what force is pulling up on the 4kg block?

Then, since you know the acceleration of the 4kg block you can solve for T₁.