How Do You Calculate Friction Force in a Two-Mass System?

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SUMMARY

The calculation of friction force in a two-mass system can be expressed as fk = m(a + g) - Ma, where m represents the mass of the hanging block, M is the mass of the object on the plane, a is the acceleration, and g is the acceleration due to gravity. The discussion emphasizes the importance of correctly defining the positive and negative directions in the system to avoid errors in the tension (T) calculations. Proper decomposition of forces and substitution are critical steps in deriving the correct expression for friction force.

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Homework Statement



http://img406.imageshack.us/img406/6092/testdd5.th.jpg http://g.imageshack.us/thpix.php


find the fk in terms of M,m,a

Homework Equations





The Attempt at a Solution



So what I got in the end result after decomposing the forces on each object and then do a substitution is :

fk = m(a+g) - Ma,

where m is the mass of the hanging block and M is the mass of the object in the plane. Is this wrong?
 
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I think your expression for T is incorrect. It may have to do with defining + and - directions.

In your +/- convention: if "a" is positive, do the blocks accelerate to the left & up, or to the right & down?
 

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