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Skier traveling uphill with and without friction

  1. Dec 12, 2014 #1
    1. The problem statement, all variables and given/known data
    If the coefficient of kinetic friction in the previous problem was actually 0.11 and the slope 30 degrees, to the nearest meter how far up the hill does he go?

    **the problem prior was: A skier traveling at 31.9 m/s encounters a 12 degree slope. If you could ignore friction, to the nearest meter, how far up the hill does he go? (my answer was 250m up the hill)**

    2. Relevant equations
    Sum of the forces in the y-axis = Fn - Fgy = 0
    Sum of the forces in the x-axis = Ff + Fgx = ma

    3. The attempt at a solution
    I figured acceleration = Fnet / mtotal
    therefore, acceleration = ((.14*mg*cos30)+(mgsin30)) / m
    then the m's would cancel and it would just be..
    a = (.14*g*cos30)+(gsin20)
     
  2. jcsd
  3. Dec 12, 2014 #2

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    ... and, your question is what?
     
  4. Dec 12, 2014 #3
    well what I thought the solution was, was incorrect. so I was looking for some guidance.
     
  5. Dec 12, 2014 #4

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    What forces contribute to deceleration of the skier?
     
  6. Dec 12, 2014 #5
    Just friction
     
  7. Dec 12, 2014 #6

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    ... and, what else?
     
  8. Dec 12, 2014 #7
    gravity?
     
  9. Dec 12, 2014 #8

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    Friction and gravity. Correct. In what directions are these forces acting?
     
  10. Dec 12, 2014 #9
    friction is opposite of the skiers motion, parallel to the surface & gravity is straight down
     
  11. Dec 12, 2014 #10

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    The surface is inclined 30° to the horizontal; how does this affect the gravitational force?
     
  12. Dec 12, 2014 #11
    It increases it...?
     
  13. Dec 12, 2014 #12

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    I'll give you a conditional "yes:" if the inclination to horizontal is 0, what is the gravitational force? and, if the inclination is 90°, what is the gravitational force?
     
  14. Dec 12, 2014 #13
    Wat is the correct answer?
    I get it as 87.13m
     
  15. Dec 12, 2014 #14
    If i's 0, the Gravitational force is equal to mass*9.8. If it's 90, I'm not exactly sure
     
  16. Dec 12, 2014 #15

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    Think again, if the skier hits a horizontal stretch, how much effect does gravity have on his velocity?
     
  17. Dec 12, 2014 #16
    Oh, none because Gravity is in the y axis and the skiers motion is in the x... So, does that mean at 90° gravity would cause him to decelerate?
     
  18. Dec 12, 2014 #17

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    Yes. Now, by how much does gravity decelerate as a function of the surface inclination?
     
  19. Dec 12, 2014 #18
    Yes . the gravity ,actusly it's sin component will cause him to decelerate. Besides he is not moving in x axis.
     
  20. Dec 12, 2014 #19
    Would it be -9.8?
     
  21. Dec 12, 2014 #20

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    Tip the surface 1 degree at a time from horizontal to vertical; for each increment of increase in the slope, how much does the effect of gravity increase?
     
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