Two books are lying on top of each other on a table. The upper book has a mass m1 , and(adsbygoogle = window.adsbygoogle || []).push({});

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 [tex]F> \mu_s(m_1+m_2)g[/tex] and then once it is going we must ensure that [tex] \mu_1 m_1g > F > \mu_d(m_1+m_2)g[/tex]

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

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

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

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