**Problem**
Suppose you are holding a heavy physics book upright between your

hands as shown in the figure to the right. The mass of the book is 4.00 kg.

When your right hand applies a force of 50.0 N normal to the book

as shown, the book remains at rest.

b.)What is the minimum possible value of the coefficient of

static friction between your hands and the book? Assume the

coefficient of static friction between your left hand and the book

is the same as the coefficient of static friction between your right

hand and the book.

**Known information**
n1=50N

m=4.00kg

Fnet=0

**Free Body Diagram** **Attempt at a solution**
$\displaystyle x:n2-n1=0 (1)$

$\displaystyle y:Fs1+Fs1-mg=0 (2)$

$\displaystyle Fs≤µsn (3)$

$\displaystyle (1) =>n2=n1=50N$

$\displaystyle (3) =>Fs=µ(50)$

$\displaystyle (2) => 100µ=mg$

$\displaystyle (2) => µs=(4*9.80)/100$

$\displaystyle (2) => µs=.392$

The concept I'm wondering about is the minimum value of the coefficient of static friction. Was I right to set Fs=µn after I had figured out that the normal forces are the same in magnitude? If not I'm not really sure how to go about this.