# Kinematics - Find theta with Coefficient of Friction?

I recently found a problem that looked like this:

A box sits on a horizontal wooden ramp. The coefficient of static friction between the box and the ramp is .30. You grab one end of the ramp and lift it up, keeping the other end of the ramp on the ground. What is the Angle between the ramp and the horizontal direction when the box begins to slide down the ramp?

The only thing this question gives me is the Coefficient of static friction between the box and the ramp. I don't think it's enough to solve the problem, is this true?

Equations Related:

$F_f=μ_sN$

$N=mg$

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## 2 Answers

Since my answer was deleted, I will say two things. First, rethink your normal force equation. Second, try using a rotated reference frame.

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Thanks I got a good look at your answer so I think I can get it from there thanks! +1 – Nate-Wilkins Sep 7 '12 at 21:36

The inverse tangent of the coefficient of static friction is $17^{\circ}$.

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While this is an approximately true statement (rounding to 2 digits), the derivation leading up to your getting this answer might be an invaluable addition to your answer. – Kyle Kanos Apr 13 '14 at 15:40