# Homework Help: Momentum and horizontal speed

1. Nov 9, 2008

### *intheclouds*

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

When tossed upward and hit horizontally by a batter, a .24kg softball recieves an impulse of 2.7 N*s. With what horizontal speed does the ball move away from the bat?

2. Relevant equations

Here are all the equations that were in our notes for this section.
p (momentum) There was triangle P and triange t in my notes, so I wrote "change in"

p=mv
f=ma
f*"change in"t="change in"p
f*"change in"t=mvf-mvi
"change in" P=mvf-mvi
3. The attempt at a solution

I really was not sure what equation I should use because I didnt really know what the impulse was. I chose f*"change in"t=mvf-mvi.
2.7 N*s= (.24kg)(0m/s)-(.24kg)(v)
I got v=-11.25m/s. I know this was wrong, but Im not sure which equation I was supposed to use or if I entered the information correctly in to the equation. Any help would greatly be appreciated.

2. Nov 9, 2008

### asleight

You can treat this as a collision.

3. Nov 9, 2008

### *intheclouds*

A collision? What type of equation is that?

4. Nov 9, 2008

### asleight

$$m_1\texbf{v}_{i,1}+m_2\textbf{v}_{i,2}=m_1\textbf{v}_{f,2}+m_2\textbf{v}_{f,2}$$

5. Nov 9, 2008

### *intheclouds*

So, what would the 2.7 N*s be considered?

6. Nov 9, 2008

### asleight

What are the units of Ns?

7. Nov 9, 2008

### *intheclouds*

Im not really sure. I think it is Neutons*second. Im pretty sure it is the impulse.

8. Nov 9, 2008

### asleight

1 N = 1 kg*m/s/s.

So, 2.7 N*s = 2.7 kg*m/s.

So, the impulse has a "mass" and a "velocity."

The ball isn't moving in the x-direction so its initial velocity is 0. Solve, the impulse goes away.

9. Nov 9, 2008

### *intheclouds*

ok so in that equation you gave me:

(.24kg)(0m/s)+(.24kg)(0m/s)=(.24kg)(v)+.24(v)??

Its all going to work out to be 0? I am really confused. I know you are trying so hard to help me, but Im lost... =]

10. Nov 9, 2008

### asleight

0.24kg ( 0 m/s ) + Impulse = 0.24kg ( V m/s ).

11. Nov 9, 2008

### *intheclouds*

Oh wow so I was really close with my first answer...It was just negative and I needed it to be positive! Thank you. =]

12. Nov 9, 2008

### asleight

You're welcome.