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

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SUMMARY

The discussion focuses on calculating the horizontal distance traveled by a skier starting from rest on a 20m high, 20° slope with a coefficient of kinetic friction (μk) of 0.210. The skier's total distance traveled down the slope is calculated to be 95.2m, but the horizontal distance is determined to be 40.3m after considering the geometry of the slope. The solution involves using trigonometric functions to find the length of the horizontal component of the slope and applying the work-energy principle to relate the forces acting on the skier.

PREREQUISITES
  • Understanding of basic physics concepts including work-energy principles
  • Knowledge of trigonometry, specifically sine and cosine functions
  • Familiarity with kinetic friction and its calculations
  • Ability to manipulate equations involving potential and kinetic energy
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  • Study the work-energy theorem in detail, focusing on non-conservative forces
  • Learn how to apply trigonometric functions to solve physics problems involving slopes
  • Explore the concept of kinetic friction and its impact on motion
  • Investigate the relationship between potential energy and kinetic energy in different scenarios
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This discussion is beneficial for physics students, educators, and anyone interested in understanding the dynamics of motion on inclined planes, particularly in relation to friction and energy conservation.

Sequence1123
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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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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.
 
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.
 

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