Vertical spring - elevator question

  1. A mass is attached to a spring supported from the ceiling of an elevator. We pull down on the mass and let it to vibrate. If the elevator starts to accelerate(fixed accelerate) upward,

    1) How the maximum velocity changes?
    2) How the amplitude changes?
    3) How the total energy changes?

    I think the amplitude and maximum velocity does not change. Because the acceleration doesn't change the net force but only slide down the equilibrium point. Am i right?
     
  2. jcsd
  3. Hootenanny

    Hootenanny 9,681
    Staff Emeritus
    Science Advisor
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    I would agree with your choice with respect to the amplitude. However, in terms of the maximum velocity, it depends on your frame of reference, what are you measuring the velocity relative to.

    P.S. We have Homework Forums for all your textbook questions.
     
  4. ___
    |M|
    ===
    \_\
    /_/
    \_\
    _|_|
    |....| /\
    |....| .|
    |....| .| moving upward
    |__.|
     
  5. Hootenanny

    Hootenanny 9,681
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    Your diagram is wrong, the mass is hanging down from the ceiling, inside the elevator, but thanks for your contribution anyway...
     
  6. Hootenanny

    Hootenanny 9,681
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    Edit: It wouldn't actually make any difference to the answer, but it's best not to confuse the matter :smile:
     
  7. oops D=

    __________________
    [tex]
    | \amalg| \cdot \cdot \cdot \cdot \mp \cdot \cdot \cdot \cdot | \amalg |
    [/tex]
    [tex]
    | \amalg| \cdot \cdot \cdot \cdot \bigcap \cdot \cdot \cdot \cdot | \amalg |
    [/tex]
    [tex]
    | \amalg| \cdot \cdot \cdot \cdot |M| \cdot \cdot \cdot | \amalg |
    [/tex]
    [tex]
    | \amalg| \cdot \cdot \cdot \cdot \bigsqcup \cdot \cdot \cdot \cdot | \amalg |
    [/tex]
    [tex]
    | \amalg| \cdot \cdot \cdot \cdot \cdot \cdot \cdot \cdot \cdot \cdot | \amalg | \Uparrow Moving Up
    [/tex]
    [tex]
    | \amalg| \cdot \cdot \cdot \cdot \cdot \cdot \cdot \cdot \cdot \cdot | \amalg |
    [/tex]
    [tex]
    | \amalg| \cdot \cdot \cdot \cdot \cdot \cdot \cdot \cdot \cdot \cdot | \amalg |
    [/tex]
    [tex]
    | \amalg| \cdot \cdot \cdot \cdot \cdot \cdot \cdot \cdot \cdot \cdot | \amalg |
    [/tex]
    [tex]
    | \amalg| \cdot \cdot \cdot \cdot \cdot \cdot \cdot \cdot \cdot \cdot | \amalg |
    [/tex]
    __________________
     
    Last edited: Apr 22, 2008
  8. it is releative to elevator. But honestly i can not explain with equations. My choice is completely instinctive. By te way, it would be nice to see the pictures with post. Latex is hard for figures.
     
  9. Hootenanny

    Hootenanny 9,681
    Staff Emeritus
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    Then you are correct, if your measuring the velocity of the mass with respect to the elevator. Obviously, if the velocity is measured relative to some other 'fixed' point outside the elevator then this will not be the case.
     
  10. I want to understand the effects of adding force and adding mass while it is vibrate. As you are approved, additional force on motion is not change the amplitude and maximum velocity. Now I wonder, how the mass change the amplitude and max velocity?

    Now there is not an elevator. The same spring and mass attached to the ceiling of a door instead of an elevator and vibrating. While the mass in bottom position, an additional mass attached to other one suddenly. What happens now? I think, as previous problem, the equilibrium point slides down. The amplitude will not change because net force was not change. But maximum velocity will reduce because period will increase and distance was not change. Am I right now?
     
  11. Hootenanny

    Hootenanny 9,681
    Staff Emeritus
    Science Advisor
    Gold Member

    I agree.
    I'm not sure about your reasoning, but I agree with your conclusion.
     
  12. I mean period proportional with mass. If mass increase period will too. Now, if amplitude the same as before then the distance for quarter period is the same too. So I think, distance the same, if time increased then average velocity must reduce.

    As I understood you agree with about maximum velocity reduce. But I can not calculate these. Any suggestion?
     
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