00:01
Alrighty, so we have a problem here at hand that involves a ski patrol lowering an individual down slope.
00:11
It's a very steep slope.
00:13
Perhaps these people are outback country skiing and something went wrong.
00:21
Here is my just quick, very quick and humble illustration of this.
00:28
Here is the angle here of 60 degrees.
00:36
All right.
00:38
The end.
00:38
I'm going to model as just this square.
00:42
I don't need to draw anything crazy here.
00:45
All right.
00:47
And we have a few things going on here.
00:50
We have that tension force going upward.
00:55
As the ski patrol lowers this individual down, you have their weight here.
01:02
I should want to say force of gravity or weight.
01:06
You have a normal force in this direction.
01:12
Not very important for this problem, but i'm going to sketch it out anyway.
01:16
And think about the velocity is going down this way, so there's also going to be a frictional force right here.
01:25
F sub -k.
01:27
All right.
01:29
So let's figure out the work done by all the forces here, and then we want to figure out the total work done at the end.
01:35
So first and foremost, let's do the work done by friction.
01:37
See if we can figure that out.
01:40
So we're going to do work.
01:44
Work of friction.
01:47
And this will equal m .g.
01:55
Cosine, excuse me, 60 degrees.
02:00
And this comes from, we're solving for this normal force here, is you're going to have a gravity vector here.
02:10
This is fg cosine theta.
02:15
And this is fg sign data.
02:21
So for a normal force you have to have, or for a frictional force you have to have, the weight, which for us is force of gravity, which is mg multiplied by the cosine of the angle here.
02:32
And then you have to multiply that by the coefficient, of friction, muse of k...