# Force and Momentum problems

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1. Mar 15, 2015

### HelpMePLz

1. The problem statement, all variables and given/known data
A catcher stops a .250kg ball traveling at 100km/hr in .19s.
a. Calculate the change in momentum of the baseball [-6.9ns]
b. Calculate the force the catcher applies to the baseball [-36.5n]

2. Relevant equations
△p=m△v
f△t=m△v

3. The attempt at a solution
a. △p=m△v
△p=m(vi-vf)
△p=mvi-mvf
△p=(.25kg*100m/s)-(.25kg*0m/s)
△p=25ns

b. F△t=m△v
F=m△v-△t
F=((.25kg*100m/s)-(.25kg*0m/s))-(.19s)
F=24.81n

2. Mar 15, 2015

### RaulTheUCSCSlug

In your attempt you have 100m/s but in your question, you have 100km/hr, you see the difference? Looks like you need to do a conversion.

3. Mar 15, 2015

### phyzguy

You need to pay more attention to the units. Getting the units right in these problems is usually the most difficult part. 100 km/hr is not the same as 100 m/s.

4. Mar 15, 2015

### HelpMePLz

Yes! Thank you so much. I will be careful with the units.
And attempt to solution B, I was using an Impulse formula and I made a mistake.
When you try to solve for the Force. You must divide time from the force.
So It would be,
F(.19s)/.19s=(.25kg*27.78m/s)/.19s
F=36.55 N

5. Mar 15, 2015

### phyzguy

I think this is now correct.