Pulley Question: Clarifying Fnetx Calculation

[jesuslovesu]

http://img135.imageshack.us/img135/3314/yeaheg1.th.png

I was wondering if someone could clarify this for me.
(this system of accelerating, the block on the right is heavier)
I know that Fnetx = T.

However, I'm a little confused about why Fnety should be Fw - T as opposed to T - Fw

When I was doing the free body diagram, for the y coord: T points up and Fw points down, so I was thinking since the standard coord system has up as +y and down as -y then Fnety = T - Fw, unfortunately it seems that it's necessary to reverse that.

 

[BishopUser]

probably reversed so that acceleration comes out as a positive value for both blocks.

 

[kyle8921]

Thank you for your question. It is important to understand how to calculate Fnetx (net force in the x-direction) and Fnety (net force in the y-direction) in order to accurately analyze the motion of an object.

In this specific scenario, it is important to remember that the pulley system is accelerating in the x-direction, which means that there must be a net force acting in that direction. This net force is equal to the tension force (T) in the rope.

In terms of Fnety, we must consider the forces acting on the block in the y-direction. As you correctly pointed out, the tension force (T) is acting upwards, while the weight of the block (Fw) is acting downwards. In order to accurately calculate Fnety, we must consider the direction of the coordinate system. In this case, the positive y-direction is upwards, while the negative y-direction is downwards. This means that the weight (Fw) should be considered a negative force, as it is acting in the opposite direction of the positive y-axis. Therefore, the correct calculation for Fnety would be Fw - T.

I hope this clarifies your confusion. It is important to always consider the direction of the coordinate system when calculating forces in different directions.