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Homework Help: HELP A dynamics problem

  1. Oct 21, 2008 #1
    HELP!!!A dynamics problem

    1. The problem statement, all variables and given/known data
    In a carnival ride called the Rotor, people stand against the inside wall of cylindrical chamber. when the chamber rotates with a sufficiently high angular velocity, the floor of the chamber is lowered and the people "stick" to the wall. the coefficient of static friction between a person and the wall is mu(s)=0.5 and the radius of the chamber is r=3.5m.
    what is the minimum angular velocity, omega, of the chamber (in revolutions per minute) that will keep the people from sliding down the wall?

    3. The attempt at a solution

    two unknown variables
    therefore, we need to find the acceleration
    Frictional force=mu(s)*m*g
    mu(s)=0.5 g=9.8
    frictional force=0.5*m*9.8
    frictional force=ma
    sub the a I got into a=(omega)^2*radius to find omega

    however, while i was trying to find the frictional force, there are two unknown variables, which are frictional force and the mass. I think that i can solve this question as soon as I know the mass for the person...can anyone teach me how to find the mass of the person?

    Thank you for helping me.
    Last edited: Oct 21, 2008
  2. jcsd
  3. Oct 21, 2008 #2
    Re: HELP!!!A dynamics problem

    You are correct that you need the mass of the person. If you can't find the mass of the person , give your answer in terms of "m" and mention that "m" is the mass of the person.
  4. Oct 21, 2008 #3
    Re: HELP!!!A dynamics problem

    What you are saying is that I will not get a numerical answer for this question, instead i will have a variable in my answer, right?
    I wish my teacher will not mark this as a wrong answer^^thanks
    by the way,so there is no way to find the mass, right?
  5. Oct 21, 2008 #4
    Re: HELP!!!A dynamics problem

    I don't think you need the mass of rider to solve this problem because it cancels out. This is a statics problem i.e. the rider is not moving. Do a free body diagram on the rider with all the forces defined (hint: I see 4 forces). Sum of the forces in X-direction is 0 and sum of all the forces in Y-direction is 0. Solve for u.
  6. Oct 22, 2008 #5
    Re: HELP!!!A dynamics problem

    Yes, I see it now. The mass should cancel out because the gravitational force, the centripetal force, and the force of friction should all depend linearly on mass.
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