(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement:

The coefficient of friction between the 3.00 kg block and surface in the figure below is 0.400. The system starts from rest. What is the speed of the 5.00 kg ball when it has fallen 1.10 m? The picture "below" depicts the 3.0 kg block on the table, attached to a string that is connected to a pulley at the end of the table and is also connected to the hanging 5.0 kg ball.

2. Relevant equations

PEg: mgh

KE: .5mv^2

Wnc = Change in PEg + Change in KE

Wnc (Distance that non-conservative factor is acting upon system) X (Force that this non-conservative factor is applying)

3. The attempt at a solution

So I assumed that this is a Work Non-Conservative problem because friction is involved. The problem states that the 5.00 kg ball has fallen 1.1 m, and since it is attached by a string to the 3.00 kg block, I assumed that the 3.00 kg block slid along the table 1.1 m. This would be the distance of the non-conservative factor. The force of the non-conservative factor would be equal to the Coefficient of friction X the normal force (in this case, (0.4)(3.0 kg)(9.81m/s^2). This gave me 12.9492.

Next, I assumed that the final potential energy of the 5.0 kg ball would be zero (because i defined the point 1.1 m below it's starting point as PE = 0), therefore the change in PE (PEf-PEi) would be -mgh. Since the ball is starting from rest, there is no initial KE, so I set my equation up as 12.9492 = -mgh + .5mv^2

Obviously, I come up with a negative answer with this. I guess I could define my h value as negative, but I've never had to do that before, and something tells me it would be a bit out of the ordinary to have to start doing that now...I'm not really sure what I'm doing wrong. Any helpful insight would be greatly appreciated! Thanks a mil!

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# Homework Help: Non-Conservative Work systems coupled with friction.

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