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What maximum power must the motor provide?

  1. Jun 26, 2011 #1
    1. A loaded ore car has a mass of 950 kg and rolls on rails with negligible friction. It starts from rest
    and is pulled up a mine shaft by a cable connected to a winch. The shaft is inclined at 30.0°
    above the horizontal. The car accelerates uniformly to a speed of 2.20 m/s in 12.0 s and then
    continues at constant speed. (a) What power must the winch motor provide when the car is
    moving at constant speed? (b) What maximum power must the motor provide? (c) What total
    energy transfers out of the motor by work by the time the car moves off the end of the track,
    which is of length 1 250 m?
    ( Ans : (a) 10.2 kW (b) 10.6 kW (c) 5.82 MJ )

    2,power = (mass x acceleration x distance)/ time
    = (950kg x (2.2/12=0.183m/s^2) x distance )/ 12s

    how to find the distance??



    3. The attempt at a solution
     
  2. jcsd
  3. Jun 26, 2011 #2

    Doc Al

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    Staff: Mentor

    Re: kinematic

    I'm not sure which part you are attempting to solve. Starting with part a, what's the force exerted by the cable? What power must it exert?
     
  4. Jun 26, 2011 #3
    Re: kinematic

    i am finding this answer (a) What power must the winch motor provide when the car is
    moving at constant speed?
     
  5. Jun 26, 2011 #4

    Doc Al

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    Staff: Mentor

    Re: kinematic

    So answer my question: What force is exerted by the cable? And how does force relate to power?
     
  6. Jun 26, 2011 #5
    Re: kinematic

    pulling force.....power = workdone / time, workdone = force x distance
     
  7. Jun 26, 2011 #6

    Doc Al

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    Staff: Mentor

    Re: kinematic

    OK, so what's the pulling force?
     
  8. Jun 27, 2011 #7
    Re: kinematic

    dont know
     
  9. Jun 27, 2011 #8

    Doc Al

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    Staff: Mentor

    Re: kinematic

    You'll have to figure it out. Hint: constant speed.
     
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