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How fast is the rod moving after it has traveled 8.00 m down the rails?

  1. Oct 21, 2009 #1
    1. The problem statement, all variables and given/known data
    An electromagnetic rail gun can fire a projectile using a magnetic field and an electric current. Consider two parallel conducting rails, separated by 0.530 m, which run north and south. A 49.0 g conducting rod is placed across the tracks and a battery is connected between the tracks, with its positive terminal connected to the east track. A magnetic field of magnitude 0.750 T is directed perpendicular to the plane of the rails and rod. A current of 2.00 A passes through the rod.
    If there is no friction between the rails and the rod, how fast is the rod moving after it has traveled 8.00 m down the rails?

    2. Relevant equations

    a=(IL(([mu0(I))/(2\pi*r)))/m
    v=sqrt{2ad}

    3. The attempt at a solution

    (2(.530)(4pi-7(2))/(2pi(.53))/.049 = 1.63e-5
    sqrt{2*1.63e-5*8}=.016

    this answer is wrong. can you please tell me what i am doing wrong and help me out?Thanks.
     
  2. jcsd
  3. Oct 21, 2009 #2

    Delphi51

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    Homework Helper

    Sweet, I don't recognize that formula! Can you derive it from basic formulas for us? I would expect you to use Fm = I*L*B in this problem - the formula for the magnetic field causing a force on a current.
     
  4. Oct 21, 2009 #3
    i got the answer, thanks for trying to help
     
  5. Oct 21, 2009 #4

    Delphi51

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    Homework Helper

    Sorry, I'm still not with you. I see you are using F = ma but why not
    F =ILB? Where does the mu and pi come from? I would begin with
    F = ma
    ILB = ma
     
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