# How to calculate angle given coefficent of friction

## Homework Statement

two objects are suspended on a platform one weighs 10 kg and the other weighs 20 kg, the coefficent of static friction is 0.4

## Homework Equations

how to find angle each of the objects start to slide

## The Attempt at a Solution

OK so Us=Fs/Fn
0.4= Fs/Fn
Fg=9.8(10) for the 10 kg object
using the vertical and horizontal components of the fg vector i get
Fn= ma cos(theta)
Fs= ma sin(theta)
U=fs/fn
0.4=sin(theta)
cos(theta) mass and acceleration cancel out
this is where i get stuck because i have theta over theta they should cancel out and i will be left with a broken equation :( any help would be appreciated.

Also if mass cancels out how am i supposed to get different angles for each of the boxes which weigh different amounts?

## The Attempt at a Solution

rock.freak667
Homework Helper
You should have for motion that Fs≥μFn

so you have mgsinθ ≥ μmgcosθ. (the minimum angle of theta would be when they are equal)

Which gives you a simple relation with θ and μ.

You should have for motion that Fs≥μFn

so you have mgsinθ ≥ μmgcosθ. (the minimum angle of theta would be when they are equal)

Which gives you a simple relation with θ and μ.

i dont understand how you would isolate theta without it canceling out or being 1

rock.freak667
Homework Helper
i dont understand how you would isolate theta without it canceling out or being 1

Remember the identity tanθ = sinθ /cosθ ?