How Is the Mass of Block B Calculated in a Friction-Affected Pulley System?

[martyk]

Homework Statement

In figure 6-36, two blocks are connected over a pulley. The mass of block A is mA and the coeffcient of kinetic friction between A and the incline is Uk. Angle of the incline is theta. Block A slides down the incline at constant speed. What is the mass of block B? Express your answer in terms of the variables given.

http://img121.imageshack.us/img121/9748/fig636.gif

Homework Equations

F = ma

The Attempt at a Solution

Taking acceleration to be 0, because speed is constant. And that T1 = T2, i came to the answer of

[m1gsin(theta) - m1gcos(theta)Uk] / g = mass of the 2nd block

Can I get a verification

 

[w3390]

Yes, that is correct.

 

[tomcue]

on this answer?

Your solution looks correct. By setting the acceleration to 0, you are accounting for the effect of friction on the block's motion. Since the blocks are connected by a pulley, the tension in the string is equal on both sides, allowing you to equate the forces acting on each block. Your expression for the mass of block B takes into account the weight of block A, the normal force from the incline, and the frictional force. Well done!