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The end of a ski jump(projectile motion)

  1. Jun 30, 2013 #1
    a ski jumper leaves the ski track moving in the horizontal direction with a speed of 25.0 m/s. The landing incline below him falls off with a slope of 35.0 degrees. where does he land on the incline?

    I already know how to use formulas to plug and chug to get an answer. I need to know why the answer is the only answer. what is the physical reasoning behind it because geometrically, the vector can be as long as it wants to be without changing that angle. What is the reasoning behind what the maximum magnitude the vector can have? how am i suppose to know this? is maximum magnitude the magnitude that is only before exceeding the magnitude that will force the skier into certain death? is it the snow that determines the limit? the ramp? what is it? i dont see it at all! we only get one angle so the triangle can be as big as it wants to be!
     
  2. jcsd
  3. Jun 30, 2013 #2

    Borek

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    Which vector?
     
  4. Jun 30, 2013 #3
    the Resultant vector. draw the picture. omg xD

    actually, they are all freaking varibles xD. all 3 of them.
     
    Last edited: Jun 30, 2013
  5. Jun 30, 2013 #4

    Borek

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    Still no idea what you are talking about. To be honest, from your description I am not convinced you know how to solve the problem. Geometrically for this particular set of data there is only one solution, period.
     
  6. Jun 30, 2013 #5

    prove it.
     
  7. Jun 30, 2013 #6
    Perhaps I'm misunderstanding the question, but if a skier goes off a jump with a known velocity, then their path through space is determined. Isn't it clear that he can only land in one particular spot on the ramp?
     
  8. Jun 30, 2013 #7
    yeah, i guess so. but the resultant vector, and the components of the resultant vector are variables.

    so how do i find the one and only answer when the distance can be anything?

    like, i can say he lands 6.5 m away. i can also say he lands 7m away. which one is it? it varies with the height of the snow. how am i suppose to only get exactly one precise finite answer when the 3 sides of the triangle are variables?

    i can take off as much snow as i want or add as much snow as i want, which will change the vertical and horizontal distance while keeping the angle the same at all times. you cant get a side with just geometry xD. cant complete a triangle with just one given angle.
     
  9. Jun 30, 2013 #8
    Whoops.
     
  10. Jun 30, 2013 #9

    Borek

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    Take a look here:

    attachment.php?attachmentid=59996&stc=1&d=1372624054.png

    There is only one point where the skier can land.
     

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  11. Jun 30, 2013 #10
    aha, tangent. ok, im convinced.
     
  12. Jun 30, 2013 #11
    wait nvm, it can still be any ratio of x and y :(
     
  13. Jun 30, 2013 #12
    lol, i saw that xD. you solve it the same way the text book does but i still dont get it. i need to know that given that angle, it can only be at that spot whether the heights change.
     
  14. Jun 30, 2013 #13

    Borek

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    Heights of what?

    Please try to analyze the drawing I posted. Vector shows initial velocity if the skier. After the jump he follows the thin line and lands on the slope. Your task is to find where the trajectory intersects the slope.
     
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