Yet another two-block system question. I guess I don't understand this still.

1. Mar 8, 2010

Bensky

1. The problem statement, all variables and given/known data
See attempt at solution. It has everything.

2. Relevant equations
F_net = ma (net force)
W = mg (weight)
f_k = u_k * N (frictional force - kinetic)

T is the tension force.

3. The attempt at a solution

See attachment below. I realize I just posted a problem related to a two block system. I got help on the last problem and thought I understood it completely, but this time I'm REALLY not sure what I'm missing. I checked over the coordinate system and all the signs in the problem and thought all my steps made sense. Am I simply missing a force?

The answer I should be getting is u_k = 0.25, but I get 0.583 instead.

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Last edited: Mar 8, 2010
2. Mar 8, 2010

rl.bhat

For 10 kg block g*sinθ and ax are in the same direction. So in that equation you have to equate it to -m*ax.

3. Mar 8, 2010

Bensky

Thank you, that did give me the correct answer. Are you saying the acceleration should be negative on block A since it is traveling in the -x direction (left)?

4. Mar 8, 2010

rl.bhat

The mass is moving in the direction of g*sinθ. In the equation you have taken g*sinθ -ve, so ax also -ve.

5. Mar 8, 2010

Bensky

What is "ve"?

EDIT: Nevermind, you mean -ve = "negative" haha. I'm a little slow tonight, nevermind! I understand, thanks.