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!

Rotating Disk

  1. May 3, 2010 #1
    1. The problem statement, all variables and given/known data
    A thin, 50.0 g disk with a diameter of 8.00 cm rotates about an axis through its center with 0.190 J of kinetic energy. What is the speed of a point on the rim?


    2. Relevant equations
    [tex]C = \frac{1}{2}MR^2[/tex]
    [tex]K_{rot}=\frac{1}{2}I\omega^2[/tex]


    3. The attempt at a solution
    Since the formula for kinetic rotational energy is [tex]K_{rot}=\frac{1}{2}I\omega^2[/tex], and the constant for the moment of inertia for a solid disk with the axis of rotation about it's diameter is [tex]C = \frac{1}{2}MR^2[/tex], I substituted the I in the second equation with the first equation, resulting in the following:

    [tex]K_{rot}=\frac{1}{2}(\frac{1}{2}MR^2)\omega^2[/tex]

    Substituting the values that I was supplied with in the problem statement, I came up with this equation:

    [tex]0.190=\frac{1}{2}(\frac{1}{2}(0.05)(0.04)^2)\omega^2[/tex]

    Solving for [tex]\omega[/tex], I ended up with [tex]\omega \approx \pm 97.5[/tex], which was determined to be incorrect.

    Any help would be extremely appreciated.
     
  2. jcsd
  3. May 3, 2010 #2
    It asks for the SPEED of a point on the rim. It does not ask for the angular speed.
     
  4. May 3, 2010 #3
    I figured it was something like that, so shortly after posting the initial topic, I tried [tex]v=r\omega[/tex] as [tex]v=(0.04)(97.5)[/tex] which results in the correct answer of 3.9. Originally I recieved an answer that was something like 360 (I must have entered a wrong number or something into the calculator) so I ignored it. Then after you posted and backed up my thoughts, I tried again and got the correct answer. Thanks!
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Rotating Disk
  1. Rotating Disks (Replies: 5)

  2. Rotation of a Disk (Replies: 2)

  3. Rotating disks (Replies: 7)

  4. Rotating Disk (Replies: 6)

Loading...