# Magnitude and direction.

1. Sep 22, 2005

### twofish

Hi all,
I'm new here and am having a problem interpreting a homework question, hope i can explain it correctly.
The question is below.

"One ball goes along the x axis and collides with a stationary ball of equal mass in a collision that is not head on. How does the y component of each velocity compare afterwards? Give both magnitude and direction."

"When ball A is rolling along the x axis there is no initial vertical momentum or y component, therefore the vector sum of the final vertical (Y) components of the two balls must be zero. "

What's got me hung up is the magnitude and direction part of the question.
Since I'm not really given any numbers to work with I'm unsure how to answer the second part of the question.
Can I assume that they are looking for the magnitude of the velocity, in which case I would answer va = (pa)/(ma) for ball a, and similar for ball b.
Or do they want the magnitude of the vectors, in which case I would have to incorporate cos θ = (pa)/p and sin θ = (pb)/p
Thanks,

Last edited: Sep 22, 2005
2. Sep 22, 2005

### Diane_

You're absolutely right that the y-component of the momentum must be zero. Now - you have two balls of equal mass. What can you say about the y-component of their velocities (both the magnitude and the direction) if the y-momentum is to cancel out? Note: You won't be able to give a numeric answer for the speeds, but you can say how they compare. Hint hint.

Last edited: Sep 22, 2005
3. Sep 22, 2005

### twofish

Hrm ..okie, well I'll try working that angle.
Thanks much!