Work done by friction on a skier and resulting distance the skier travels

In summary, a skier starting from rest on a 20m high, 20° slope with a coefficient of kinetic friction of 0.210 will travel a horizontal distance of 40.3m before reaching the bottom of the slope. This can be found by finding the length of the bottom of the triangle formed by the slope of the hill and the horizontal, and subtracting it from the total length traveled.
  • #1
Sequence1123
2
0

Homework Statement


A skier starts from rest on a 20m high, 20° slope. μk=0.210
Find the horizontal distance traveled by the skier.
From this, for the equations below we know that:
yf = 0
vi = 0
vf = 0

Homework Equations


Wnet = Wnc + Wg = ΔKE
Wnet = -fkd
Wnc = ΔKE + ΔPE
Wnc = ΔKE + mg(yf - yi)
KE = 1/2mv2
PE = mgy
fk = μkmg

The Attempt at a Solution


So I went with the work of a non-conservative force
Wnc = (KEf - KEi) + (PEf - PEi)
Wnc = (1/2mvf2 - 1/2mvi2) + (mgyf - mgyi)
From given, I eliminated all 0 quantities, leaving me with
Wnc = -mgyi
Then plugged in Wnet = -fkd = -μkmgd so,
kmgd = -mgyi
eliminated like terms (m, g):
kd = -yi
and solved for d
d = yik
and plugged in the knowns
d = 20m/0.210
d = 95.2m
I realize this is the distance traveled from the top of the hill to the end of motion, but all they want is the horizontal distance, so now I have to solve for the distance traveled from the top of the hill to the bottom of the hill. The only thing I think that changes between the above work and the distance from the top to bottom is the final velocity which will be nonzero.
So my question is, how do I find the distance traveled from the top of the hill to the bottom?
Or am I going about this wrong? Is there a more direct way to find just the horizontal distance traveled?

Oh I should add, the answer given by the book is 40.3m
 
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  • #2
Sequence1123 said:

Homework Statement


A skier starts from rest on a 20m high, 20° slope. μk=0.210
Find the horizontal distance traveled by the skier.
Is this the full statement of the problem?

I'm guessing that after the skier gets to the bottom of the slope, she skis over a horizontal stretch of ground? Perhaps it's that horizontal distance that they want.
 
  • #3
Doc Al said:
Is this the full statement of the problem?

I'm guessing that after the skier gets to the bottom of the slope, she skis over a horizontal stretch of ground? Perhaps it's that horizontal distance that they want.

AH! I figured it out...

I had to find the length of the bottom of the triangle formed by the horizontal and the slope of the hill. sin20° = 20/x (where x is the hypotenuse, or the length of the slope of the hill)
from that I got x ≈ 58.5m
Then,
cos20° = x/58.5m (where x is the length of the bottom of the triangle)
x ≈ 54.9m
then subtract that from the total length traveled by the skier, 95.2m - 54.9m = 40.3m which is the answer given by the book.
 

What is work done by friction?

Work done by friction is the force that opposes motion between two surfaces that are in contact with each other. In other words, it is the energy that is lost due to the resistance of the surface.

How does friction affect a skier?

Friction can have both positive and negative effects on a skier. It can help the skier maintain control and slow down, but it can also create resistance and make it more difficult for the skier to move forward.

How does the distance a skier travels relate to work done by friction?

The distance a skier travels is directly related to the work done by friction. The more friction that is present, the more energy is lost and the shorter the distance the skier will travel. On the other hand, less friction means more energy is preserved and the skier can travel a greater distance.

What factors affect the amount of work done by friction on a skier?

The amount of work done by friction on a skier depends on various factors such as the type of surface the skier is on, the weight and speed of the skier, and the angle of the slope. Additionally, factors such as the temperature and humidity can also affect the amount of friction present.

Can friction be eliminated completely for a skier?

No, it is not possible to completely eliminate friction for a skier. Friction is a natural force that occurs whenever two surfaces are in contact with each other. However, techniques such as waxing the skis and using smoother surfaces can help reduce the amount of friction and make it easier for the skier to move.

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