Finding gravitational potential energy

[jaron]

Homework Statement

The distance between the sixth and the eleventh floors of a building is 30.0m. The combined mass of the elevator and its contents is 1350 kg.

a) find the gravitational potential energy of the elevator when it stops at the eighth floor, relative to the sixth floor.

(the answer in the back of my textbook is : 1.5x10^5 J )

Homework Equations

now i am thinking E=mgh, but i am also thinking that i an going to need to do something about the work formula. i know that w=F"d, and when the force is acting in the opposite direction, you must use W=F"d cos 180'. but this might be totally irrelevant.

The Attempt at a Solution

with this equation i am getting: E=1350(9.81)(30) E=397305 J

 

[LowlyPion]

The distance between the 6th and 11th is 30 meters.

The distance between the 6th and 8th then is 12 meters isn't it?

 

[jaron]

yeah, thanks. i feel like an idiot about the question now..
forgot to consider that fact that the 30m was for the whole height and not for floor 6-8.