# Homework Help: Force needed to move a box.

1. Feb 26, 2009

### wcbryant87

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

The weight of the crate is 875 N. You push it with a force of magnitude 300 N but it doesn't move

What is the magnitude Fp of the minimum force you need to exert on the crate to make it start sliding along the floor? Let the coefficent of the static friction $$\mu$$s betwen the crate and the floor be 0.56 and that of kinetic friction, $$\mu$$k, be 0.47

2. Relevant equations

3. The attempt at a solution

I tried solving it by using the formula fk = $$\mu$$kn but it told me that I'm going about the problem wrong. It says that I need to study the condition for which the crate ceases to be at rest, that is, the condition for which static friction ceases to be valid. I used kinetic friction though, so I don't know what to do now.
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Feb 26, 2009

### Delphi51

Use the static coefficient of friction in your formula.
Once it has started moving, the lower dynamic coefficient comes into play and a smaller force will suffice to keep it moving.