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Power physics question

  1. Jan 5, 2008 #1
    1. The problem statement, all variables and given/known data

    Determine the power required to pull a body of mass m up a smooth plane
    inclined at an angle a to the horizontal at a constant speed Vo. Explain why
    it is unnecessary to specify the direction in which the applied force is acting.

    2. Relevant equations

    Power= work done /time
    work done= force * distance
    Force= mg

    3. The attempt at a solution

    Power= mg/ time
     
  2. jcsd
  3. Jan 5, 2008 #2

    Doc Al

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    Staff: Mentor

    mg is the force, not the work done.
     
  4. Jan 5, 2008 #3
    Power= work done /time
    work done= force * distance
    Force= mg

    power= mgd
     
  5. Jan 5, 2008 #4
    now you forgot the time element
     
  6. Jan 5, 2008 #5

    Doc Al

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    Do it step by step. If the angle is "a", what force is required to move the body at constant speed? Say you move the object a distance "d" up the incline, how much work is required? How much time is required, if the speed is v0? What's the power required?
     
  7. Jan 5, 2008 #6
    Power= work done /time
    work done= force * distance
    Force= mg

    Power= force * distance / time
    = mg * d /t
    = veloctiy *mg
     
  8. Jan 5, 2008 #7

    Doc Al

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    Your answer should be in terms of the angle and the speed.
     
  9. Jan 5, 2008 #8
    power= vsine mg
     
  10. Jan 5, 2008 #9

    Doc Al

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    Right. [itex]P = mg \sin (a) v_0[/itex].
     
  11. Jan 5, 2008 #10
    doc...can you show me how to arrive to get sin in the solution..i know its by resolving..but can you pelase provide details thanks
     
  12. Jan 5, 2008 #11

    Doc Al

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    Since the object moves at constant velocity, the net force on it must be zero. Since it moves along the incline, examine forces in that direction. Since the component of gravity parallel to the incline is [itex]mg\sin\theta[/itex] downward, the applied force must have an equal component parallel to the incline pointing upward. Make sense?

    Note: Since the object moves parallel to the incline, only force components parallel to the incline contribute to work done.
     
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