# Homework Help: Problem with Tension

1. Feb 7, 2010

### David999

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

Well for a lab we did, there's a 3kg mass hanging over a pulley, attached to a 5.4kg brick by a rope, causing the brick to accelerate over a horizontal surface. I have no idea how I'm supposed to calculate the tension.

Oh, and the force of friction is 12.01 N.

2. Relevant equations

F=ma?

3. The attempt at a solution

I don't even know where to begin.

Thank you!

2. Feb 7, 2010

### SArnab

The total tension in the rope will be the net force acting on the brick. If you draw a free-body diagram, you see that the net force is equal to the frictional force subtracted from the tension caused by the 3kg mass.

$$T_{net}$$ = $$F_{net}$$ = ($$T_{mass}$$ - $$F_{friction}$$)

3. Feb 7, 2010

### Spinnor

Two forces (weight force minus tension force) act on the mass causing it to accelerate downward and two forces (tension force minus friction force) act on the brick causing it to accelerate horizontally at the same rate as the mass.

4. Feb 7, 2010

### David999

You're a lifesaver! Thank you so much!

I had actually drawn a FBD and got tension= Fnet, but the there was a question on the lab which through me off... the equation you gave solves everything!