# Angular momentum

1. Jun 26, 2011

### vlio20

Hi to all,

the question is:

http://ufu.co.il/files/dyzh41xkp5amsfjpv4dk.png

the two sticks clash and stick one to the other, the plane is smooth friction.
the momentum of one stick (in it's own center of mass is 0.5*L^2*m).

the length of the sticks is L and the mass is m, the vertical's stick speed is v.

I have to find the angular speed (w- omega) that both sticks will rotate in, I have manged to do this with the angular momentum preservation law, and I would like to know how to this with energy preservation law.

tnx
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Jun 26, 2011

### vlio20

the energy is not the same before and after the clash- it is not an elastic clash

3. Jun 26, 2011

### tiny-tim

welcome to pf!

hi vlio20! welcome to pf!
you can't , it isn't!

(mechanical) energy is never conserved unless the question says so

in this case, it obviously isn't conserved, because the two bodies stick together, so it's a perfectly https://www.physicsforums.com/library.php?do=view_item&itemid=38"

https://www.physicsforums.com/library.php?do=view_item&itemid=53" and energy are enough to solve a problem … any extra equation (like a geometrical constraint) means that something has to go, and that's always the energy equation

Last edited by a moderator: Apr 26, 2017
4. Jun 26, 2011

### ehild

Last edited by a moderator: Apr 26, 2017
5. Jun 26, 2011

### tiny-tim

oops!

oops!

6. Jun 26, 2011

### vlio20

yes I have understand my mistake after I posted it.
the collision is a plastic and not elastic

tnx