Dynamics Conservation of linear and angular momentum

[Dublin]

Attached file shows where my problem occurs. I understand how to get the angular momentum just before the collision. But what confuses me is is within the square. Why mvg(r) is only on the left hand side when I've had similar equations with it on both sides. Why is Ig used and why isn't Ib used for rotational energy since isn't the ω that's used is about Ib.

 

[tiny-tim]

Hi Dublin!

Why mvg(r) is only on the left hand side when I've had similar equations with it on both sides. Why is Ig used …

You could use mv_Gr + I_Gωon the RHS also …

but it's much simpler to use I_Aω !

… and why isn't Ib used for rotational energy since isn't the ω that's used is about Ib.

erm … no, ω is the same about any point

 

[Dublin]

so why does mvr + Igw= Iaw? what is r suppose to represent? i thought it was just the distance of the mass center to the point of which the moment is being rotated about in this case Ia

 

[Dublin]

i think i figured it out thanks