# Homework Help: Descending elevator stops determine displacement of mass on spring

1. Apr 18, 2013

### jm1379

Hey guys i am very stuck any help appreciated. I do not know where to start.

The equations used need to be derived from first principles and accurate free body diagrams drawn.

An elevator moves downwards at a constant velocity v0. While descending, at a particular height (assuming t=0), the velocity of the elevator decreases until zero in a time t0. Assuming the velocity is a parabolic function of v0 [1-(t/t0)^2]. Determine the displacement x of the mass m for t less than or equal to t0. Assuming z= x - u

Here is a link to the image
http://img5.imageshack.us/img5/6618/springi.png [Broken]

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2. Apr 18, 2013

### voko

First select some reference frame.

3. Apr 18, 2013

### jm1379

So Assume downwards is + to try and eliminate negative numbers?

4. Apr 18, 2013

### voko

"downwards +" is a not a reference frame.