Physics
posted by Elle on .
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

Your approach looks OK.
Check for any errors in copying the problem or any math errors. 
Wtotal = [(1020)(9.8)6678] 18.4
= 61051.2J
61051.2J = 1/2 (6500)x^2
x = 4.33m
STill wrong :( Help 
The displacement of the safety spring has to be considered in the total potential energy of the elevator car.

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 
For the roots of the quadratic I got
+4.875
3.854