# Homework Help: What impulse was exerted?

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1. Feb 6, 2016

### x2017

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

2. Relevant equations
ΣF=ma
FF=μFN
impulse=ΣFΔt
momentum=mv
ΣFΔt=mΔv

3. The attempt at a solution

This is where I got stuck... How can I solve for impulse without time or velocity? Is there a way to manipulate the equations to love for either time or velocity?

2. Feb 6, 2016

### Buzz Bloom

Hi x:

As I read the problem statement, the time to use is 1.5 seconds, and the force is calculated using FF=μFN.

Also, WRT (a), I think your teacher would like momentum in the units kg m/s.

Hope this helps.

Regards,
Buzz

3. Feb 6, 2016

### x2017

Okay, thank you! I wasn't sure if the question meant friction while the athlete was exerting a price on the rock or afterwards (which I don't have a time for).
& thanks for the tip about the units!

c) impulse=ΣFΔt
= (18.64N)(1.5s)
=27.96Ns Is this supposed to be negative because friction is acting in the negative direction?

d) Yikes, still stuck on this one! Does it have anything to do with this equation? v'={M[V(1+e)-ev]+mv}/M+m

4. Feb 6, 2016

### Buzz Bloom

Hi x:

My guess is that your teacher is likely to prefer a minus sign, but that's just a guess.

I confess I have trouble parsing the equation in this linear form.

You have the momentum from (a). You also have the friction force you used to calculate (c). How much time will it take for the friction force to reduce the momentum to zero? How far will the stone travel in that amount of time? Since the velocity is being reduced linearly, what is the average velocity of the stone during the time between F1 becoming zero 0 and velocity becoming 0?

Regards,
Buzz