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A simple yet annoying problem

  1. Apr 22, 2010 #1
    1. The problem statement, all variables and given/known data
    An 80kg man stands on an elevator what force is exerted on the elevator if it is rising with a

    constant velocity of 4.0 m/s. (take account of grvitational acceleration g=9.8m/s^2)
    2. Relevant equations
    F=ma



    3)attempt to solve

    the time and distance is not given so I could not find the aceleration at all if it were it woul be merely simple addition of acceleration multiplied by the mass

    F=m(g+a) what i want to know is that how can u calculate it with just the velocity?
     
  2. jcsd
  3. Apr 22, 2010 #2

    Doc Al

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    Staff: Mentor

    If the velocity is constant, what's the acceleration?
     
  4. Apr 22, 2010 #3
    then the acceleration is constant aswell.... but whats the value of the acceleration
     
  5. Apr 22, 2010 #4

    Doc Al

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    Staff: Mentor

    I want you to tell me the value of the acceleration. Just think about the definition of acceleration.

    Hint: It's trivial, once you realize it.
     
  6. Apr 22, 2010 #5
    -___- it would be the same as when it is stationary? 9.8m/s^s.....but why? if its correct
     
  7. Apr 22, 2010 #6

    Doc Al

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    Staff: Mentor

    Careful. When moving at constant velocity you'll have the same acceleration as when stationary. But that's not 9.8 m/s^2!

    9.8 m/s^2 is the acceleration something has when it's falling. Not when it's just sitting there.
     
  8. Apr 22, 2010 #7
    Is the velocity is constant, then there is no acceleration. Correct?
     
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