# Homework Help: Pulling out a book (friction problem)

1. Feb 26, 2010

### center o bass

Two books are lying on top of each other on a table. The upper book has a mass m1 , and
the lower book has a mass m2 . The coeﬃcient of static fric-
tion between the books is µ1 . The coeﬃcient of static friction
between the book and the table is µ2 and the coeﬃcient of
dynamic friction between the book and the table is µd . You
pull on the lower book with a horizontal force F .

(a) How large must F be for you to start pulling both books
along the table.

(b) How large must F be for you to pull out only the lower
book?

(a) I reasoned that to get the books going at all we must have that $$F> \mu_s(m_1+m_2)g$$ and then once it is going we must ensure that $$\mu_1 m_1g > F > \mu_d(m_1+m_2)g$$

(b) To get the book going we must again have that $$F> \mu_s(m_1+m_2)g$$, but then once it is going $$F > \mu_d(m_1+m_2)g \wedge \mu_1 m_1g$$.

Is this the correct reasoning here? We must split the problem up in two parts right?

2. Feb 27, 2010

### center o bass

Noone who can help me with this?

3. Feb 27, 2010

### PhanthomJay

You seem to have a lot of extra stuff in your response. Part a asks for the value of F required to move the books. Please provide one answer only for the value of F in part a and correct any typos.

For part b, again provide one answer and correct any typos. Whats that ^ in your equation??