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Homework Help: Help on homework please force

  1. Oct 24, 2007 #1
    help on homework please....force

    hey, i dont know if what i did for this question is correct, because the equation i found in my textbook may not be the right one to use.

    A 5.0g bullet leaves the muzzle of a rifle with a speed of 320m/s. What force (assumed constant) is exerted on the bullet while it is traveling down the .82m-long barrel of the rifle?

    i used the equation:
    (m(v^2)) / 2d =F

    (.005kg*(320m/s)^2 )/ (2*.82m) =F
    F= 312.2N

    Is this close to being correct?
  2. jcsd
  3. Oct 24, 2007 #2
    There are two ways to do this problem, the easiest is with energy (which is what I assume you did), I deleted a post doing the other way :redface:

    Take work done on the bullet and equate to kinetic energy:

    [tex]Fd = \frac{1}{2}mv^2[/tex]
    [tex]F = \frac{mv^2}{2d}[/tex]

    Your answer looks good to me :approve:
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