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Impulse how to figure out?

  1. Jan 2, 2009 #1
    Hello... new to the forum and not sure where to post, I see a warning everywhere lol Hope I'm not in the wrong spot.

    I haven't been in school in well over a decade, but I'm the kind of guy that went out and got math books on my own because I was jonsing to do some math... it's fun for me. But right now I'm just trying to remember the concept of Impulse and how it was calculated and well, it's been a while. (I did search through the forums before posting btw, didn't find my answer)

    I remember watching my teacher throw an egg at a sheet and suggesting throwing it at a wall, then pointing out the difference in impact was measured in Impulse... right?

    If I wanted to figure out the difference in force, say the egg would feel, hitting wall A and wall B (the sheet)... how would I measure that? Is that even a valid question? I'm confused.. Difference in acceleration during each impact = different amount of time = difference in force... so if I know the distance the egg travels while being absorbed into the sponginess (also knowing it's initial velocity) vs. the other impact (0 since it is an instant impact..), can I find out the force involved?

    If that's too vague I can input more... or too complicated it can be simplified lol I just want to "get it" again and be able to figure out different scenerios if you see what I'm getting at...

    Thanks for any help!
     
  2. jcsd
  3. Jan 2, 2009 #2

    HallsofIvy

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    You can certainly find out the average force on the egg (finding the force at each instant would be far more difficult). I would suggest using "conservation of energy". If the egg has mass m and initial speed v, its kinetic energy is (1/2)mv<sup>2</sup>. After it has stopped its kinetic energy is, of course, 0 so the change in kinetic energy is (1/2)mv<sup>2</sup> and that must be equal to the work done on the egg: force times distance. If F is the (average) force with which the egg hits the wall and x is "the distance the egg travels while being absorbed into the sponginess" then Fx= (1/2)mv<sup>2</sup> so F= (1/2)mv<sup>2</sup>/x.
     
  4. Jan 2, 2009 #3
    Excellent! Thank you! It was that x = distance factor I was messing up in my head.. I was thinking I needed to input the difference in time rather then distance... man I miss doing this stuff. Thanks again!
     
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