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!

Angular Speed of a ball of clay

  1. Feb 4, 2010 #1
    1. The problem statement, all variables and given/known data
    A ball of clay of mass m travels with velocity v in a path tangent to a disk of radius R and mass M as shown in the figure. The clay collides with the desk tangentially to its outer rim (a totally inelastic collision) and the clay and disk begin to spin about the axis.

    What is the final angular speed of the clay and disk? (Don't forget to include the mass m after the collision.)


    2. Relevant equations
    L = M x V x R
    MVR = I(tot) x W
    W = (M x V x R ) / I


    3. The attempt at a solution

    I(tot) = MR^2 + (2/5)MR^2
    MR^2 [1+(2/5)] = 7/5MR^2
    W = MVR/[(7/5)MR^2]
    W = 5V/5R

    Is this correct? What are the units?
     
  2. jcsd
  3. Feb 5, 2010 #2

    ehild

    User Avatar
    Homework Helper
    Gold Member

    The moment of inertia for a disk is 1/2 MR^2. You used that of a sphere.

    When the units are not specified you do not need to give them, you have to solve the problem symbolically.

    If you want to check your result, use the SI units, kg for mass, m for length, m/s for velocity. The unit of the angular momentum is then kg m^2 s^-1, the unit of moment of inertia is kgm^2, and the unit of w is 1/s.

    ehild
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook