# Homework Help: Calculating Momentum

1. Feb 24, 2006

### Huskies213

Can anyone help with this ???
A 220g ball falls vertically downward, hitting the floor with a speed of 2.4 m/s and rebounding upward with a speed of 1.8 m/s.
A.) Find the magnitude of the change of the balls momentum (up=positive)
i used p=mv; (.22kg)(1.8) = .396 as well as (220g)(1.8)=396

B.) Find the change in the magnitude of the balls momentum. (Neg. value=decrease in magnitude)

Can anyone help on this 2 parts?

2. Feb 24, 2006

### anjor

i guess its right the way you have done it....

3. Feb 24, 2006

### topsquark

I'm not sure what the difference between a and b is supposed to be...

Anyway, $$\mathbf{\Delta p} = \mathbf{p_f} - \mathbf{p_i}$$. Remember that these are vectors, so in your coordinate system, the initial p is negative, your final p is positive.

Note:
Watch the units! Your first calculation is good, but your second is wrong since you are using g, not kg.

-Dan