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Gravitation potential energy question help

by jbjohnybaker
Tags: earth, gravity, mgy, physics, potentital
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jbjohnybaker
#1
Apr20-11, 07:22 PM
P: 19
1. The problem statement, all variables and given/known data

A 68.5-kg skier rides a 2.56-km ski lift from the base of a mountain to the top. The lift is at an angle of 13.9 to the horizontal. Determine the skier’s gravitational potential energy at the top of the mountain relative to the base of the mountain.

2. Relevant equations
Eg= mg delta y


3. The attempt at a solution

eg = (68.5)(9.81)(2560)
= 1720281.6 J

The answer in the textbook is 4.13x10^5 J :S
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eczeno
#2
Apr20-11, 07:36 PM
P: 242
hello,

you have not accounted for the angle. the ski lift does not go straight up, it goes up a slope.
jbjohnybaker
#3
Apr20-11, 07:42 PM
P: 19
Quote Quote by eczeno View Post
hello,

you have not accounted for the angle. the ski lift does not go straight up, it goes up a slope.
I have been taught that "the value of delta y is the vertical displacement of the object. This means that the horizontal path of an object follows in changing its vertical height is not significant" :S

eczeno
#4
Apr20-11, 07:45 PM
P: 242
Gravitation potential energy question help

that is correct, but you have the wrong value for delta y. the lift travels a total distance of 2.56 km, but that is not the change in altitude, that is how long the cables are.
jbjohnybaker
#5
Apr20-11, 07:49 PM
P: 19
Quote Quote by eczeno View Post
that is correct, but you have the wrong value for delta y. the lift travels a total distance of 2.56 km, but that is not the change in altitude, that is how long the cables are.
is it right?

eg = (68.5)(sin13.5)(9.81)(2560)
eczeno
#6
Apr20-11, 07:50 PM
P: 242
looks good.
jbjohnybaker
#7
Apr20-11, 07:53 PM
P: 19
thank you very much.
eczeno
#8
Apr20-11, 07:58 PM
P: 242
cheers.


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