Conservation of Angular Momentum Help

[Speedking96]

Homework Statement

Below is the question:

I only have an issue with the last step of the problem. Why wouldn't you factor in the translational AND rotational energy of the ball and then solve for maximum height?

 

[jbriggs444]

The translational kinetic energy of the ball is the rotational kinetic energy of a system consisting of the ball alone when using a reference axis such that the ball's radial velocity is zero.

 

[Stephen Tashi]

Why wouldn't you factor in the translational AND rotational energy of the ball and then solve for maximum height?

In a real life problem you'd have to do that. In this problem, you have no information that would allow you to calculate a specific number for the rotation rate for the 5 kg ball. You don't know the diameters of the balls. The book expects you to treat them as "point masses".

Without considering friction or the deformation of the objects,, how could the bar impart any rotation to the 5 kg ball?

 

[Speedking96]

Alright, I understand. Thank you.