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Ohm's Law Application Problem

  1. Jul 31, 2010 #1
    1. A car, 5 km distance from a station, take 100 A over a 100 mm hard drawn copper trolley wire having a resistance of 0.270 ohm per km. The rail and ground return has a resistance of 0.06 ohm per km. If the station voltage is 750 V, what is the voltage of the car?

    2. Relevant equations
    I think this are the relevant equations..
    I assume that they are connected in series..
    so Icar=Irail
    i don't know what to do with 0.0270 and 0.06 ohms per km..

    3. The attempt at a solution
    I tried solving for Vcar by Vcar=I[car]*R[car]
    where in Icar=100 A and Rcar is 0.0270 ohm/km(1km/1x10^6mm)(100mm)

    Vcar=2.7x10^-4.. which is obviously wrong because V[station]=750V and its impossible that the car only takes 2.7x10^-4 V.. Pls help me thanks.
  2. jcsd
  3. Jul 31, 2010 #2


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    Staff Emeritus
    Science Advisor
    Gold Member

    You are given all the information you need to compute the total resistance of the wire and the rail. Once you have the resistance it is easy to compute the voltage drop of the wire and rail. You can then find the voltage at the car.
  4. Aug 1, 2010 #3
    Are the wire and rail in series or in parallel with the car?? What must I do with the voltage of the station??
    Last edited: Aug 1, 2010
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