Elastic Collision between ball and pivoted rod

[erisedk]

Homework Statement

This is a solved problem--
http://web.mit.edu/8.01t/www/materials/InClass/IC_Sol_W13D1-10.pdf

Homework Equations

The Attempt at a Solution

In the solution, they conserve energy and angular momentum. Can I conserve linear momentum? Also, can I use coefficient of restitution (as e=1)?

 

[Satvik Pandey]

I think we can not conserve linear momentum because if we consider rod and ball as a system then an external force acts on it(at P). But we can use e=1 here.