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Homework Help: Newton's Thrid Law Question

  1. Mar 16, 2010 #1
    1. The problem statement, all variables and given/known data
    I have a mass of 65kg. If I jump off a 120-cm-high table, how far toward me does Earth move during the time i fall?

    2. Relevant equations
    F=ma


    3. The attempt at a solution
    Had a shot using f=ma but couldn't get the answer.

    P.S
     
  2. jcsd
  3. Mar 16, 2010 #2

    kuruman

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    What is the force that you exert on the Earth? Knowing this force, can you calculate the Earth's acceleration?
     
  4. Mar 23, 2010 #3
    ok, i had another try of this question and i went W=mg which is 68 * 9.8 i get the force 666.4N then what should i do next?
     
  5. Mar 23, 2010 #4

    kuruman

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    If 666.4 N is the force that the Earth exerts on you, what the force that you exert on the Earth?
     
  6. Mar 30, 2010 #5
    the same because of Newton's Third Law, so i found the acceleration by doing the following:
    Mass of Earth is 5.97 * 10^24 (according to the book)

    637 = (5.97 *10^24)a
    a=1.06*10^-22 m/s^2

    now how do i find how far toward me does Earth move during the time i fall?
     
  7. Mar 30, 2010 #6

    kuruman

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    How many seconds does it take you to fall 1.20 m to the surface of the Earth with an acceleration of 9.8 m/s2? In that same amount of time the Earth "falls" towards you with an acceleration of 1.06x10-22 m/s2. Use the kinematic equation to find the distance.
     
  8. Mar 30, 2010 #7
    thanks i know how to do it now.
     
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