# Impulse with snowballs hitting a wall

1. Nov 16, 2016

### Jrlinton

1. The problem statement, all variables and given/known data
Two average forces. A steady stream of 0.250 kg snowballs is shot perpendicularly into a wall at a speed of . Each ball sticks to the wall. Figure 9-49 gives the magnitude F of the force on the wall as a function of time t for two of the snowball impacts. Impacts occur with a repetition time interval , last a duration time interval , and produce isosceles triangles on the graph, with each impact reaching a force maximum . During each impact, what are the magnitudes of (a) the impulse and (b) the average force on the wall? (c) During a time interval of many impacts, what is the magnitude of the average force on the wall?

2. Relevant equations

3. The attempt at a solution
a
J=Favg*t
200N/2*.01seconds=1kgm/s
J=Δp=0-.25kg*4m/s= -1 kgm/s
The impulse should be positive since its asking for the impulse on the wall and not the snow ball correct? I should have had
.25kg*4m/s-0= 1 kgm/s ?
b,
Since the graph is of isosceles triangles I can just divide the max F by 2 to get 200N/2=100N
Or use:
Favg=m*v/t
=(.250kg*4m/s)/.01s
=100 N
c.
should just be the maximum force divided by the time interval between the peak of two impacts?
200N/.05s
4000N/s?

2. Nov 16, 2016

### Jrlinton

For c:
Favg=m*v/t?
=(.250kg*4m/s)/.05s
20N

3. Nov 16, 2016

### haruspex

Apart from the mass of a snowball, you did not state any input numbers. I deduce you were told the impact velocity, the impact duration, the impact separation, and, redundantly, the peak force. As far as I can tell, your working is all correct.

4. Nov 16, 2016

### Jrlinton

I should have looked at how the copy/paste had actually performed when posting the problem