Interesting Inelastic Collision

[stanli121]

Homework Statement

Consider a translating and rotating rigid disk. As it movies, it just tips the top of a rod that is initially at rest. The puck sticks to the rod, forming a rigid body that looks like a
popsicle that after the collision moves on as one rigid body. I did the calculations to show that KE is not conserved but I'm now wondering how KE is not conserved if the contact point of the disk has zero relative velocity with respect to the rod?

Homework Equations

The Attempt at a Solution

Thus far, I am thinking that there is some work done by friction at the mutual contact patch that allows the new rigid body to rotate in such as way as to conserve angular and linear momentum. There is no pivot through the rod so that does not exert a force/torque. Something like 'the rod bends' or 'the disk deforms' seems less than satisfactory. Any ideas as to explain the loss in KE would be much appreciated.

 

[tiny-tim]

hi stanli121!

the rotation is irelevant …

the kinetic energy is lost for the same reasons as when a non-rotating object hits the back of something and sticks to it