# Equilibrium Problem

1. Jun 9, 2010

### inky

1. The problem statement, all variables and given/known data

2. Relevant equations

Summation F(x)=0

Summation F(y)=0

Summation tau=0

3. The attempt at a solution

I know how to calculate the problem but I don't know the last part of the solution why the examinar choose mu(min)=1. Please help me.Thank you.

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2. Jun 10, 2010

### kuruman

You have already seen that the force of friction is the same 4N at all points. That's what's required to keep the system at equilibrium. Imagine starting with a large μ and reducing it gradually. Slipping will occur at the point where the maximum value that static friction can have (=μ R) goes just below the value 4 N first. So if you write

μR = 4 N,

at which of the three points A, B and C μR falls below 4 N first as you make μ smaller?

3. Jun 12, 2010

### inky

Thank you very much for explaination.Firstly I don't understand so I read many times your concept. Now I understand. I really appreciate you. Sorry for replying late.