Solving Two Blocks Friction Homework

[magasiki]

Homework Statement

A small box of mass m_1 is sitting on a board of mass m_2 and length L. The board rests on a frictionless horizontal surface. The coefficient of static friction between the board and the box is mu_s. The coefficient of kinetic friction between the board and the box is, as usual, less than mu_s.

Throughout the problem, use g for the magnitude of the acceleration due to gravity. In the hints, use F_f for the magnitude of the friction force between the board and the box.

Find F_min, the constant force with the least magnitude that must be applied to the board in order to pull the board out from under the the box (which will then fall off of the opposite end of the board).
Express your answer in terms of some or all of the variables mu_s, m_1, m_2, g, and L. Do not include F_f in your answer.

Homework Equations

F_f=mu_s*N
N=mg

The Attempt at a Solution

So i know that the force of friction is mu_s*mg, and i know that the force needs to exceed that, but i don't know what i have to do next to proceed to the answer the book wants. Please help, soon.

 

[Mindscrape]

I don't know what answer your book wants either, but it looks like it wants some sort of algebraic answer. I would say that Newton's second law is a good place to start. What conditions need to happen for the board to be pulled out?