# Homework Help: Vertical spring - elevator question

1. Apr 22, 2008

### Volcano

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. Apr 22, 2008

### Hootenanny

Staff Emeritus
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 https://www.physicsforums.com/forumdisplay.php?f=152" for all your textbook questions.

Last edited by a moderator: Apr 23, 2017
3. Apr 22, 2008

### Crazy Tosser

___
|M|
===
\_\
/_/
\_\
_|_|
|....| /\
|....| .|
|....| .| moving upward
|__.|

4. Apr 22, 2008

### Hootenanny

Staff Emeritus
Your diagram is wrong, the mass is hanging down from the ceiling, inside the elevator, but thanks for your contribution anyway...

5. Apr 22, 2008

### Hootenanny

Staff Emeritus
Edit: It wouldn't actually make any difference to the answer, but it's best not to confuse the matter

6. Apr 22, 2008

### Crazy Tosser

oops D=

__________________
$$| \amalg| \cdot \cdot \cdot \cdot \mp \cdot \cdot \cdot \cdot | \amalg |$$
$$| \amalg| \cdot \cdot \cdot \cdot \bigcap \cdot \cdot \cdot \cdot | \amalg |$$
$$| \amalg| \cdot \cdot \cdot \cdot |M| \cdot \cdot \cdot | \amalg |$$
$$| \amalg| \cdot \cdot \cdot \cdot \bigsqcup \cdot \cdot \cdot \cdot | \amalg |$$
$$| \amalg| \cdot \cdot \cdot \cdot \cdot \cdot \cdot \cdot \cdot \cdot | \amalg | \Uparrow Moving Up$$
$$| \amalg| \cdot \cdot \cdot \cdot \cdot \cdot \cdot \cdot \cdot \cdot | \amalg |$$
$$| \amalg| \cdot \cdot \cdot \cdot \cdot \cdot \cdot \cdot \cdot \cdot | \amalg |$$
$$| \amalg| \cdot \cdot \cdot \cdot \cdot \cdot \cdot \cdot \cdot \cdot | \amalg |$$
$$| \amalg| \cdot \cdot \cdot \cdot \cdot \cdot \cdot \cdot \cdot \cdot | \amalg |$$
__________________

Last edited: Apr 22, 2008
7. Apr 23, 2008

### Volcano

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.

8. Apr 23, 2008

### Hootenanny

Staff Emeritus
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.

9. Apr 23, 2008

### Volcano

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?

10. Apr 23, 2008

### Hootenanny

Staff Emeritus
I agree.