# Tension Rope and Blocks Problem

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1. Apr 11, 2015

### DaveTan

1. The problem statement, all variables and given/known data
Two blocks, each with weight w, are held in place on a frictionless incline as shown in Figure. In terms of w and the angle a of the incline, calculate the tension in the rope connecting the blocks

2. Relevant equations
T = mg

3. The attempt at a solution
I cannot for figure out why the answer is Wsin(a)! I thought that since Tsin(a) = mg, T = w/sin(a)

2. Apr 11, 2015

### Coffee_

You have to look at the forces that are pulling along the surface. The force pulling downwards the slope is $F_d=mgsin(a)$, the force pulling up is just the tension $T$. For the block to be not moving along the slope these two have to be equal to eachother.

3. Apr 11, 2015

### Staff: Mentor

Hi DaveTan, Welcome to Physics Forums.

Take a close look at the geometry of a block on a slope. The weight W = Mg forms the hypotenuse of the force triangle:

4. Apr 12, 2015

### DaveTan

Thanks! But shouldn't tension be pointing in the other direction? So towards the top-right instead of bottom left?

5. Apr 12, 2015

### haruspex

Tension acts both ways (as does compression). The force it exerts on B will be up and to the right, that on A down and to the left.
By the way, the reason your original approach went wrong is that the vertical forces include a component of the normal force.