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Vertical spring - elevator question

by Volcano
Tags: elevator, spring, vertical
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Volcano
#1
Apr22-08, 02:18 PM
P: 126
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?
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Hootenanny
#2
Apr22-08, 02:36 PM
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Quote Quote by Volcano View Post
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?
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.
Crazy Tosser
#3
Apr22-08, 02:40 PM
P: 175
___
|M|
===
\_\
/_/
\_\
_|_|
|....| /\
|....| .|
|....| .| moving upward
|__.|

Hootenanny
#4
Apr22-08, 02:45 PM
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Vertical spring - elevator question

Quote Quote by Crazy Tosser View Post
___
|M|
===
\_\
/_/
\_\
_|_|
|....| /\
|....| .|
|....| .| moving upward
|__.|
Your diagram is wrong, the mass is hanging down from the ceiling, inside the elevator, but thanks for your contribution anyway...
Hootenanny
#5
Apr22-08, 03:18 PM
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Quote Quote by Hootenanny View Post
Your diagram is wrong, the mass is hanging down from the ceiling, inside the elevator, but thanks for your contribution anyway...
Edit: It wouldn't actually make any difference to the answer, but it's best not to confuse the matter
Crazy Tosser
#6
Apr22-08, 10:42 PM
P: 175
Quote Quote by Hootenanny View Post
Your diagram is wrong, the mass is hanging down from the ceiling, inside the elevator, but thanks for your contribution anyway...
oops D=

__________________
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__________________
Volcano
#7
Apr23-08, 07:21 AM
P: 126
what are you measuring the velocity relative to
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.
Hootenanny
#8
Apr23-08, 08:53 AM
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Quote Quote by Volcano View Post
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.
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.
Volcano
#9
Apr23-08, 09:20 AM
P: 126
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?
Hootenanny
#10
Apr23-08, 10:31 AM
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Quote Quote by Volcano View Post
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.
I agree.
Quote Quote by Volcano View Post
But maximum velocity will reduce because period will increase and distance was not change. Am I right now?
I'm not sure about your reasoning, but I agree with your conclusion.
Volcano
#11
Apr23-08, 03:39 PM
P: 126
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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