(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

I've got a few physics homework questions I need a bit of help with. All relate to friction.

Here's the first one:

The µs = .2 between the boxes. Mass 2 (80kg) is on an air table. What minimum force will keep mass 1 (40kg) from slipping? What is the maximum acceleration that will keep the mass from slipping?

Here's a pic I drew up with FBDs.

2. Relevant equations

0.2Fn+Fsin30=mg or 0.2Fcos30+Fsin30=mg

3. The attempt at a solution

If I solve for F I get 582. 289N but the answer I was given is 637N. Where did I go wrong? or is that the right answer? I think it's because I didn't account for mass 2 moving when the force is applied but I'm not sure how to do that.

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# Friction related problems

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