The figure shows an overhead view of a 2.50-kg plastic rod of length 1.20 m on a table. One end of the rod is attached to the table, and the rod is free to pivot about this point without friction. A disk of mass 39.0 g slides toward the opposite end of the rod with an initial velocity of 33.0 m/s. The disk strikes the rod and sticks to it. After the collision, the rod rotates about the pivot point.
(a) What is the angular velocity of the two after the collision?
What is the angular momentum of an object moving with a linear velocity, about a given point? rad/s
(b) What is the kinetic energy before and after the collision?
The Attempt at a Solution
I believe the set up would look something like this:
(Irodxwrod)i+(Idisk x wdisk)I=(Idisk+Irod)wf
The initial speed of the rod is zero, canceling that out.
MR^2/2 x V/R=(MR^2/2 + ML^2/3)wf
The problem I am having is we are not given the radius of the disk. Is it possible I am missing that the radius cancels out?
And again, with the KE, we need the radius in order to solve for angular momentum in the equation.
Thank you for any help!