Posted by **Elle** on Saturday, October 27, 2007 at 7:51pm.

The cable of an elevator of mass M = 1020 kg snaps when the elevator is at rest at one of the floors of a skyscraper. At this point the elevator is a distance d = 18.4 m above a cushioning spring whose spring constant is k = 6500 N/m. A safety device clamps the elevator against the guide rails so that a constant frictional force of f = 6678 N opposes the motion of the elevator. Find the maximum distance by which the cushioning spring will be compressed.

This is what I did but the answer was wrong!:

Wtotal = (mg- f) 18.4m

Wtotal = 1/2 kx^2

- Physics -
**Quidditch**, Saturday, October 27, 2007 at 7:59pm
Your approach looks OK.

Check for any errors in copying the problem or any math errors.

- Physics -
**Elle**, Saturday, October 27, 2007 at 8:14pm
Wtotal = [(1020)(9.8)-6678] 18.4

= 61051.2J

61051.2J = 1/2 (6500)x^2

x = 4.33m

STill wrong :( Help

- Physics -
**Quidditch**, Saturday, October 27, 2007 at 8:59pm
The displacement of the safety spring has to be considered in the total potential energy of the elevator car.

- Physics -
**Elle**, Saturday, October 27, 2007 at 9:29pm
Um are you saying

Wtotal = [(1020)(9.8)-6678] (18.4+x) ?..

In that case, I did the quadratic and got x=17.33m, but still wrong answer :( argg

- Physics -
**Quidditch**, Saturday, October 27, 2007 at 10:46pm
For the roots of the quadratic I got

+4.875

-3.854

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