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Power needed to overcome friction and gravity

  1. May 2, 2013 #1
    1. The problem statement, all variables and given/known data

    Hi all please could you take a look at this question and help me

    1) A packing case weighing 1000N is loaded onto the back of a lorry by being dragged up an incline of 1 in 5 at a steady speed of 2m/s. the frictional resistance to motion is 240N, Calculate:
    a. The power required to overcome friction

    b. The power needed to overcome gravity
    c. The total power needed


    The problem I have is i don't know what i need to do to the incline.
    Please could someone guide me

    2. Relevant equations

    Power needed to overcome friction = friction force * velocity along surface

    3. The attempt at a solution
    Part a.
    Power needed to overcome friction = friction force * velocity along surface
    Power needed to overcome force = 240N * 2m/s = 480N
    Therefore power need is 480N to overcome the friction.



    Now not sure if part a is correct also i'm stuck with part b. i dont know what to do now
     
  2. jcsd
  3. May 2, 2013 #2
    Work is defined as the product of force and the displacement in the direction of the force. For gravity that would be the vertical displacement. Think about the consequences for power.
     
  4. May 2, 2013 #3

    haruspex

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    Right number, wrong units.
     
  5. May 2, 2013 #4

    CWatters

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    For b)...

    As it goes up the slope it's height and therefore it's PE is changing. Power is the rate of change of energy.
     
  6. May 2, 2013 #5
    in my mind, incline of 1 in 5 as figured bellow
    block_on_incline.png

    a. answered.. [itex]P_{friction}=480 joule/s = 480 [/itex]watt
    b. to overcome gravity
    [itex]P_{g}=mg.sin θ v= 1000 \frac {1} {5} 2[/itex]watt

    c. [itex]P_{total}=480+200=680[/itex]watt
     
  7. May 2, 2013 #6

    haruspex

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    1. The protocol on these homework fora is to nudge people in the right direction, not write out complete solutions.
    2. Check your arithmetic.
     
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