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Homework Help: I suck at physics

  1. Sep 24, 2005 #1

    chipsdeluxe

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    i suck at physics!!!

    can someone please help me with some physics problems?

    1. A woman stands on a scale in a moving elevator. Her mass is 62.2 kg, and the combined mass of the elevator and scale is an additional 836 kg. Starting from rest, the elevator accelerates upward. During the acceleration, the hoisting cable applies a force of 9110 N. What does the scale read during the acceleration?

    2. Synchronous communications satellites are placed in a circular orbit that is 2.32 x 107 m above the surface of the earth. What is the magnitude of the acceleration due to gravity at this distance?

    i don't even know where to start. any help would be great
     
    chipsdeluxe, Sep 24, 2005
  2. jcsd
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  3. Sep 24, 2005 #2

    HallsofIvy

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    Science Advisor

    Force equals mass times acceleration. What would the scale read if the woman were standing on it while it was not accelerating?

    You know the mass of the woman, scale, and elevator. Use F= ma to find the acceleration of all of them. Now use F= ma with just the mass of the woman to find what force would give that acceleration to her alone. Add that force to here weight.

    F= GmM/r2. Add the radius of the earth to the height above the earth to find r, the satellites distance from the earth. You will have to look up G ("universal gravity constant") and M (the earth's mass). Since acceleration is a= F/m, the "m"s cancel and you don't need to use the satelite's mass.
     
    HallsofIvy, Sep 24, 2005
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