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Homework Help: Motor power in Kw

  1. May 10, 2009 #1
    1. The problem statement, all variables and given/known data

    Ok so i need to choose a motor that is capable of moving 15 tonnes (metric) over a distance of 16 m at 0.2 m/s.

    So, im guessing i need to first find the force required to move this object which would be F=m*a. Is this right???

    Now, what would be the equation to find the power required in Kw?

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. May 10, 2009 #2


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    No, f=ma is only the force needed to accelerate it upto 0.2m/s
    The power is mainly to overcome friction.
    You need to know what friction is involved, consider how hard it is to drag a 15tn rock over concrete compared to how much power you need to pull a 15tn boat.
  4. May 10, 2009 #3
    Ill give some more background. The calculations i need really don't have to go into too much detail though.

    This equation is for a crane trolley of 15 tonnes (metric) which moves along 2 beams. So, it is not a metal on metal contact. It will be a set of wheels or more accurately a rack and pinion set. Are there equations which do not take friction into account as i have been told by my lecturer that friction can be disregard.
  5. May 10, 2009 #4


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    Neglecting friction it takes no power to keep the trolley moving at any speed.
    To get it moving you have to put in energy = 1/2 m V^2, how quickly you do this (ie how long you take to accelerte it ) determines the power (power is energy/time)
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