# Homework Help: Momentum/Impulse Problem

1. Apr 30, 2007

### husky88

Hi. I was wondering if anyone could help me with this problem.

A baseball of mass 850 g travelling at 15 m/s due south is caught and thrown northwest at the same speed during a time interval of 0.85 s.
(a) What is the magnitude of the change in the momentum of the ball during this time interval?
(b) What is the direction of the change in the ball's momentum during this time interval?
(c) What are the magnitude and the direction of the impulse delivered to the ball during this time interval?

There are more questions, but I know how to do those.
I have solved the problem, but I got different answers from the answer key. I don't know what I am missing.

(a) I got this one correct 24 kg*m/s.
(b) I got 22.5° East of South. They say it is 135°, no direction specified. 135° is the angle between the two vectors. Why would that be the direction of the change in the momentum?
(c) I got 24 N*s 22.5° East of South. They say it is 24N*s 22.5° West of North. Why is the direction of the change in momentum different from the direction of the impulse? Why do I have a direction of East of South and they say it is West of North?

Any help would be greatly appreciated. Thank you.

2. Apr 30, 2007

### Fredrik

Staff Emeritus
b) My interpretation of "change" is "new vector minus old vector" (if my weight changes from x to x+20, the change is +20, not -20), so I get 22.5° west of north.

3. Apr 30, 2007

### husky88

Thank you so much.
Subtraction of vectors is very unclear to me. As to which way the resultant vector points, but I think I got it.