1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Rotational Motion of a penny

  1. Jul 23, 2010 #1
    1. The problem statement, all variables and given/known data
    A penny is placed on an LP record that is slowly accelerating up to 78 revolutions per minute. It is found that if the penny is placed at 0.080m or greater from the center, then the penny slides off the edge of the record. Find the coefficient of static friction if the mass of the penny is 0.0032kg.


    2. Relevant equations
    Ff = mu x n

    a = v2/r


    3. The attempt at a solution

    I don't know how to start. Can someone guide me please??
     
  2. jcsd
  3. Jul 24, 2010 #2
    Ok. Let us begin with this question. You are given the frequency of the LP (and thus the period as well), and you are given the mass of the penny. As you have written above,
    Frictional Force = co-eff * Normal and centripetal acceleration = v^2/r = 4Pi^2r*frequency^2. For the penny to stay on the LP, friction has to provide enough centripetal force. When the radius is too great, the velocity of the penny is too large and it flys off the LP. Thus, we are looking for:
    Force Friction = Force centripetal = mass of penny* centripetal acceleration.
    The rest is plain math and some unit conversions.
     
  4. Jul 24, 2010 #3
    thanks.

    Normal is just equal to mg, right?
     
  5. Jul 24, 2010 #4
    yes. So youll notice that the mass does not actually matter in the question since it cancels out.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Rotational Motion of a penny
  1. Rotative motion (Replies: 3)

  2. Rotational Motion (Replies: 5)

  3. Rotational Motion (Replies: 2)

  4. Rotational motion (Replies: 8)

Loading...