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Math Help - Probability question, please help!

  1. #1
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    Probability question, please help!

    This is a maths question I need to have completed today, but I don't know how to do it!

    "What is the probability that you will get hit by a fragment of a hand grenade assuming you stand 3 meters from the explosion?"
    "Assume that the grenade weights 600 grams"
    "Assume that the explosive inside weights 60 grams"
    "Assume that each fragment will weights 2 grams"

    Using only this data, how can I solve this problem?
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  2. #2
    Grand Panjandrum
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    Quote Originally Posted by RichardtheMath View Post
    This is a maths question I need to have completed today, but I don't know how to do it!

    "What is the probability that you will get hit by a fragment of a hand grenade assuming you stand 3 meters from the explosion?"
    "Assume that the grenade weights 600 grams"
    "Assume that the explosive inside weights 60 grams"
    "Assume that each fragment will weights 2 grams"

    Using only this data, how can I solve this problem?
    You can't.

    The casing mass is 600-60=540 gm, so if each fragment has mass 2 gm there are 270 fragments.

    Now we need some assumptions (which are in fact invalid). Assume the fragments fly out so that they have a uniform distribution over the unit sphere, and do not fall or decellerate etc. Then a body has an cross sectional area of about 1 sq m, a 3 m radius sphere has a surface area of 4 \pi 9 \approx 113 sq m. So the mean number of fragments that will hit you is about  270/113 \approx 2.4.

    Now assume that the number of fragments that hit you has a Poisson distribution with this mean.

    RonL
    Last edited by CaptainBlack; September 2nd 2008 at 01:29 AM.
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  3. #3
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    Hmm, I'll need to check over my notes and review the question, (I wrote down the verbal question) maybe I missed something.
    Anyways thanks for the help.
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