# Energy Problem

A84 kg skier jumper starts fro rest at the top of a 220 m hill. What is the velocity of the skier jumper, if the jump is 105 m from the bottom of the hill.

My Proof:

m=84 KG
h=105 m
Eg=84kg*9.8N/kg*105m
Eg=86436J
so Eg=Ek
86436J=1/2*85*V^2
V=45..36m/s

Is that right or Wrong?

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hage567
Homework Helper
It's wrong.

You must consider the energy he has at the top of the hill. Apply conservation of energy between that height and the height of the jump.

It's wrong.

You must consider the energy he has at the top of the hill. Apply conservation of energy between that height and the height of the jump.
i didn't understand u
can u explain me?

hage567
Homework Helper
Well for one thing, the kinetic energy the skier has at the time he reaches the jump must come from somewhere. The change in potential energy between the top of the hill and the jump is what will determine the kinetic energy at the jump. It will determine his velocity.

Why don't you think the potential energy the skier has at the top of the hill is important in finding out how much kinetic energy he has at the jump?

Well for one thing, the kinetic energy the skier has at the time he reaches the jump must come from somewhere. The change in potential energy between the top of the hill and the jump is what will determine the kinetic energy at the jump. It will determine his velocity.

Why don't you think the potential energy the skier has at the top of the hill is important in finding out how much kinetic energy he has at the jump?
can u give me proof?

hage567
Homework Helper
Tell me why you think it's wrong.

Tell me why you think it's wrong.

hage567
Homework Helper
Well you must have done your answer that way for some reason.

can u give me proof?
What kind of proof are you looking for? I'm not going to give you the answer if that's what you mean.

Have you tried to use my idea to solve this problem? What about it is giving you trouble?
Can you find the total energy of the skier when he is at rest at the top of the hill?

Well you must have done your answer that way for some reason.

What kind of proof are you looking for? I'm not going to give you the answer if that's what you mean.

Have you tried to use my idea to solve this problem? What about it is giving you trouble?
Can you find the total energy of the skier when he is at rest at the top of the hill?
Eg=mghA
Eg=84kg*9.8N/kg*220m
Eg=181104J

Eg=mghB
Eg=84kg*9.8N/kg*105m
Eg=86436J

Eg=181104J-86436J
Eg=94668J

So Eg=Ek
94668JJ=1/2*85*V^2
V=47.47m/s

Is that right or Wrong?

hage567
Homework Helper
I would say that is right.