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Spring in moving elevator!

  1. Sep 26, 2011 #1
    1. The problem statement, all variables and given/known data

    Three masses m1 = 3.1 kg, m2 = 9.3 kg and m3 = 6.2 kg hang from three identical springs in a motionless elevator. the elevator is moving downward with a velocity of v = -2.3 m/s but accelerating upward with an acceleration of a = 4.8 m/s2. (Note: an upward acceleration when the elevator is moving down means the elevator is slowing down.) What is the force the bottom spring exerts on the bottom mass?

    2. Relevant equations

    f=-kx

    3. The attempt at a solution

    Some of my confusion lies with k. Since k is a constant is it the same value as if the elevator was motionless or does k change when the elevator moves?
     
  2. jcsd
  3. Sep 26, 2011 #2
    The spring constant k is constant in the elastic region of the spring. Assume this for your solution.
     
  4. Sep 27, 2011 #3
    Still not sure how to solve this I guess
     
  5. Sep 27, 2011 #4
    Draw your Free-Body Diagram first.
     
  6. Sep 27, 2011 #5

    SammyS

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    How is it this possible "... a motionless elevator. the elevator is moving " ?

    Follow flyingpig's advice !!!
     
  7. Sep 27, 2011 #6

    PeterO

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    I think he means the masses are motionless wrt the lift and not bouncing around - but yes free body diagram.
     
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