# Homework Help: How to find the coefficient of friction in a rotor-ride?

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1. Nov 4, 2014

1. The problem statement, all variables and given/known data
I have no values at all, so it's just going to be the variables in the relevant equations. I need to define mu using those variables.
A carousel is moving in a circle at velocity v and has a radius r. It is moving fast enough that each person with mass m is pinned against the wall and not moving. What does mu (the coefficient of friction) have to be in order for the people to not move? Define it in terms of m, g, r, or v.
I know that it has a square root involved somewhere because all the answer choices have square roots.

2. Relevant equations
friction=mu(normal force)
centripetal Force= mv^2/r
Force of Gravity=gm
3. The attempt at a solution
Centripetal force=normal force=force of friction/ mu
force of friction/ mu=mv^2/r
force of friction= force of gravity (because friction pushes up with the same amount as gravity pushes down)
mg/ mu= mv^2/r
g/ mu =v^2/r
(cross multiply)
mu*v^2= gr
mu=(gr)/(v^2)
But I know this can't be right because there's no square root.

2. Nov 4, 2014

### Staff: Mentor

Hi b! http://img96.imageshack.us/img96/5725/red5e5etimes5e5e45e5e25.gif [Broken]

What are the answer choices offered?

Last edited by a moderator: May 7, 2017