Why is the collision angle 90 degrees in a 2d collision?

[SELFMADE]

Homework Statement

Stationary ball is placed 20 degrees to the right of the moving ball's trajectory. Both balls are of same weight. Collision occurs and balls part at 90 degree angle. We measured it and it was 90 degrees on two occasions.

Explain why it is 90.

Homework Equations

Momentum conservation law?

The Attempt at a Solution

Can't think of any

 

[kuruman]

It's a collision, so yes use momentum conservation, but remember that this is a two-dimensional collision.. Is there anything else that is conserved? What do you think?

 

[SELFMADE]

Honestly if I knew I wouldn't ask.

Can someone please, at least, tell me what topic to read?

 

[SELFMADE]

Bump, anyone?

 

[kuruman]

Read about two-dimensional collisions and momentum conservation. Then read about conservation of energy. Apply these ideas to your problem.

 

[SELFMADE]

I swear to god I read the whole chapter on impulse and momentum on friday night. There was nothing about angle. I know you're not suppose to reveal direct answers but for christs sake, can I get a break?

 

[SELFMADE]

anyone?

 

[ideasrule]

It's strange that there was nothing about angle in that chapter on momentum. Momentum has to be conserved in both the x and y directions, so write out the equations for those. Energy is also roughly conserved; if it wasn't, the balls would stick together and not part. So you have three equations: two for conservation of momentum and one for conservation of energy. Solve them.

 

[SELFMADE]

momentum has to be conserved in both the x and y directions,

ok i see now