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Work done by expanding gasses on bullet

  1. Oct 6, 2012 #1
    1. The problem statement, all variables and given/known data
    A 95-g bullet is fired from a rifle having a barrel 0.540 m long. Choose the origin to be at the location where the bullet begins to move. Then the force (in newtons) exerted by the expanding gas on the bullet is 16200 + 9400x - 23750x2, where x is in meters.
    (a) Determine the work done by the gas on the bullet as the bullet travels the length of the barrel.

    (b) If the barrel is 0.96 m long, how much work is done?

    (c) How does this value compare with the work calculated in part (a)?(% difference)

    2. Relevant equations

    W = force * displacement

    3. The attempt at a solution

    after plugging in 0.54 in the force equation i got F = 14,350.5 N

    then multiplied it by 0.54 to get work and got 7.75 kJ

    same for the second part but i got both answers wrong, i thought it was a simple problem but i guess not.
  2. jcsd
  3. Oct 6, 2012 #2


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    Note that the force is a function of x. So, it is not a constant force. You need to know how to get the work done by a variable force.
  4. Oct 6, 2012 #3
    so i basically need to do the integral F dot ds and then plug in the values?
  5. Oct 6, 2012 #4


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    Yes, that's it.
  6. Oct 6, 2012 #5
    I should have realized that to begin with but thank you for all the help!
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