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Forces on boxcars

  1. Oct 27, 2009 #1
    A train consists of a 4300kg locomotive pulling two loaded boxcars. The first boxcar has a mass of 12,700kg and the second 16,300kg. Presume that the boxcar wheels roll without friction and ignore aerodynamics. The acceleration of the train is 0.578m/s^2
    a)With what force, in Newtons, do the boxcars pull on each other?

    I am confused here. Do they pull on each other with the same force? They can't since they don't weigh the same, correct?

    0.578=T/12700 T=7340.6

    0.578=T/16300 T=9421.4


    b) With what force do the locomotive and first boxcar pull on each other?

    I can use the same steps from a) for this one

    c)With what force must the tracks push on the locomotive?

    would the force be equal to the weight?
     
  2. jcsd
  3. Oct 27, 2009 #2

    Doc Al

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    Staff: Mentor

    What does Newton's 3rd law tell you?

    Don't confuse the net force on a car with the force between the cars.

    First things first. Draw diagrams of each car, showing the forces acting on it. Then apply Newton's laws as needed.
     
  4. Oct 29, 2009 #3
    a) boxcars pull on each other
    F=16300(0.578)=9421.4

    b)The locomotive pull on the first boxcar
    F=12700+16300(0.578)=16762

    c)The tracks push on the locomotive
    F=4300(9.80)=42140

    Are these formulas correct?
     
  5. Oct 29, 2009 #4

    Doc Al

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    Staff: Mentor

    The first answer is correct, but the others are not. I suggest that you label the forces--for example, F1-2, FL-1, and Ft-L--then write force equations for each car.
     
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