Homework Help: Physics

Posted by Sarah on Monday, March 8, 2010 at 3:42pm.

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.
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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, Monday, March 8, 2010 at 4:02pm
You forgot the friction.

IntialPE=finalKE+frictionwork

As an aside, your use of significant digits is lacking.
Physics - Sarah, Monday, March 8, 2010 at 5:48pm
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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