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A train of 3000 KN weight starts from rest and reached a velocity of 54 km/h after o

  1. Jun 10, 2012 #1
    Hi all

    1 ) A train of 3000 KN weight starts from rest and reached a velocity of 54 km/h after one min . if the frictional resistance of the track is 5N/KN of the train's weight . Find the tractive force developed by the engine ?

    I don't understand what is mean "tractive force " ??

    anyway I start solve the question

    w = 3000 kN
    mass = 305810
    u = 0
    v = 54 km/h

    v = u + at
    a = 0.25
    F = m X a
    F = 305810 X 0.25
    76452.5 N
     
  2. jcsd
  3. Jun 10, 2012 #2

    rock.freak667

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    Re: A train of 3000 KN weight starts from rest and reached a velocity of 54 km/h afte

    Right a = 0.25 m/s2 (Always remember to put your units).

    In the formula F=ma, a is the resultant acceleration of the mass m (Train in this case). So F is the resultant force.

    If you draw a free body diagram, what are the forces on the train? (The tractive force is essentially the force generated by the train itself).
     
  4. Jun 10, 2012 #3
    Re: A train of 3000 KN weight starts from rest and reached a velocity of 54 km/h afte

    force on the train
    1 weight
    2 frictional resistance
    3 tractive force

    now How I can find the tractive force
     
  5. Jun 12, 2012 #4
    Re: A train of 3000 KN weight starts from rest and reached a velocity of 54 km/h afte

    I don't know where is the other helper ..
     
  6. Jun 12, 2012 #5

    rock.freak667

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    Re: A train of 3000 KN weight starts from rest and reached a velocity of 54 km/h afte

    In which direction do these forces act?

    How would you find the resultant horizontal force?
     
  7. Jun 12, 2012 #6
    Re: A train of 3000 KN weight starts from rest and reached a velocity of 54 km/h afte

    I don't know how to find resultant horizontal force?

    anyway the direction for each one weight dawn , frictional resistance opposite of tractive force
     
  8. Jun 12, 2012 #7

    rock.freak667

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    Re: A train of 3000 KN weight starts from rest and reached a velocity of 54 km/h afte

    Right so let's say frictional force is going left and the tractive force is going right. The train is moving to the right. How would you calculate the value of the force that the train is moving with from these two forces?

    in other words, if we are in a tug of war competition and you are pulling with 10 N and I am pulling with 11 N, what would be the resultant force in this case?
     
  9. Jun 14, 2012 #8
    Re: A train of 3000 KN weight starts from rest and reached a velocity of 54 km/h afte

    Resultant force = tractive force - frictional force
     
  10. Jun 14, 2012 #9

    rock.freak667

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    Re: A train of 3000 KN weight starts from rest and reached a velocity of 54 km/h afte

    Right!

    So you calculated the resultant force in your first post. And they told you what the frictional force was. So you can rearrange to get the tractive force.
     
  11. Jun 15, 2012 #10
    Re: A train of 3000 KN weight starts from rest and reached a velocity of 54 km/h afte

    tractive force = Resultant force - frictional force
    = 76452.5 - 3000
    now this is correct ??
     
  12. Jun 15, 2012 #11

    rock.freak667

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    Re: A train of 3000 KN weight starts from rest and reached a velocity of 54 km/h afte

    Check the signs in your equation.
     
  13. Jun 15, 2012 #12
    Re: A train of 3000 KN weight starts from rest and reached a velocity of 54 km/h afte

    76452.5 + 3000 ... ?
     
  14. Jun 15, 2012 #13

    rock.freak667

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    Re: A train of 3000 KN weight starts from rest and reached a velocity of 54 km/h afte

    That should work.
     
  15. Jun 15, 2012 #14

    HallsofIvy

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    Re: A train of 3000 KN weight starts from rest and reached a velocity of 54 km/h afte

    Remember that the "tractive force", the force applied to the track by the locomotive, must be larger then the resultant force as it has to overcome the frictional force.

    You can write it as "Resultant force- frictional force" if you remember to treat "frictional force" as negative.
     
  16. Jun 16, 2012 #15
    Re: A train of 3000 KN weight starts from rest and reached a velocity of 54 km/h afte

    now is my answer if fully correct ... ?
     
  17. Jun 16, 2012 #16

    rock.freak667

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    Re: A train of 3000 KN weight starts from rest and reached a velocity of 54 km/h afte

    It should be.
     
  18. Jun 23, 2012 #17
    Re: A train of 3000 KN weight starts from rest and reached a velocity of 54 km/h afte

    my teacher said the answer is not correct

    and he said why you don't multiply

    5 X 3000

    I don't know what he mean ?

    and my other questions is the Resultant force
    ma + tractive force

    or only F = ma
     
    Last edited: Jun 23, 2012
  19. Jun 23, 2012 #18
    Re: A train of 3000 KN weight starts from rest and reached a velocity of 54 km/h afte

    frictional resistance of the track is 5N/KN of the train's weight
     
  20. Jun 25, 2012 #19
    Re: A train of 3000 KN weight starts from rest and reached a velocity of 54 km/h afte

    5 X 3000

    unit is Kn or N

    and my other questions is the Resultant force
    ma + tractive force

    or only F = ma
     
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