Physics
posted by Sarah .
A ski trail makes a vertical descent of 78.0 m (as shown in the figure below ). A novice skier, unable to control his speed, skis down this trail and is lucky enough not to hit any trees. If the skier is moving at 12.1 m/s at the bottom of the trail, calculate the total work done by friction and air resistance during the run. The skier's mass is 68.9 kg.

So far, I've been using
mgh+1/2mv^2=mgh+1/2mv^2 for the beginning and end of the run, so with an initial velocity of 0 and a height of 0 at the end, I get
52667.16=5043.824, the difference of which is 47623.3355J.
However, that is not the answer and I'm not sure how to continue. Any assisstance would be greatly appreciated!

Physics 
bobpursley
You forgot the friction.
IntialPE=finalKE+frictionwork
As an aside, your use of significant digits is lacking. 
Physics 
Sarah
We haven't learned how to do the friction work yet.
And I had the answer, but I forgot to make it negative. Thank you though.
And in reply to your aside, I only use significant digits in my answer.
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