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

On a box (of mass "m"), force "F" is applied at "theta" degree angle above the horizontal. The box has static friction coefficient of "u." When this force is applied, and the box remains stationary, what expression describes the frictional force?

2. Relevant equations

F=uN??

(N is normal force)

3. The attempt at a solution

I came down to 2 choices:

F=umg

or

F=uFcos(theta)

I initially thought the former, because I keep remember being drilled the equation F=uN, and about how it's all about the normal force when it comes to friction.

But then when I thought about it, forces must balance out... so if there's no net acceleration, applied force (i.e. Fcos(theta)) MUST balance out frictional force, no???

And now I'm just confusing myself.

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# Homework Help: Static friction force

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