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Homework Help: Locomotive question!

  1. Sep 25, 2006 #1
    Hi all,

    Another teaser that I have been attempting is the following:

    A Locomotive (A) pulls two tracks (B) and (C). The masses of A,B & C are 80, 25 and 20 tonne respectively. The train starts from rest and accelerates uniformally to cover 2KM in 8 minutes. Assume the resistance to motion of the locomotive and the trucks is 200N/tonne

    1. Calculate the tractive effort developed by the locomotive A.

    I have used the formula: Tractive Effort = Total resistance to motion (R) + Mass x Acceleration.

    The total resistance to motion is 200/N tonne x (80+25+20) = 25KN
    The mass is 125 Tonne
    The acceleration I have as 0.01736111 m/s using s=ut+1/2at^2.

    Therefore I have the tractive effort as 27.17K Newtons.

    Is this right???

    2. Calculate the draw-bar pull between A and B
    3. Calculate the draw bar pull between B & C

    I am struggling with 2 and 3. Could anyone give me any pointers??
  2. jcsd
  3. Sep 25, 2006 #2


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    1. Your reasoning is correct. I have not checked your numbers, but I suppose they are OK.
    2. Remember that A must pull the combined masses of B and C.
    3. The draw bar between B and C must pull the mass of C.
  4. Sep 25, 2006 #3


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    Staff Emeritus
    Science Advisor

    The acceleration of 0.01736111 m/s2 is correct assuming that locomotive and trucks are accelerating uniformly.

    As SGT mentioned, the drawbar between A and B has the masses and resistance of B and C pulling on it, and between B and C, the drawbar only pulls C.
  5. Sep 25, 2006 #4
    Ok taking this into consideration I have done the following.

    Resistance to motion = 25 tonne x 200 N/tonne = 5000N for truck b
    = 20 tonne x 200 N/tonne = 4000N for truck c

    Therefore total resistance to motion is 9000N.

    Force required to move B & C = Acceleration x mass = 781.25N

    Therefore the pull between A and B is 9000N + 781.25 = 9781.25N

    Does this seem right??

    Obviously for the pull between B & C it will be the same precedure but just taking into account the resistance & motion of C.
  6. Sep 25, 2006 #5


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    It's right.
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