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Projectile motion

  1. Apr 25, 2013 #1
    1. The problem statement, all variables and given/known data

    A particle is projected at 30 m/s from the foot of a plane which is inclined at 30o to the horizontal. The particle hits the plane at an angle perpendicular to the plane.
    Find the value of the angle of projection θ and the time taken to reach there.

    2. Relevant equations

    x=30tcosθ , and y=30tsinθ-5t^2 , where (x,y) are the coordinates of the point of impact and θ is the angle of projection, inclined with the horizontal.

    3. The attempt at a solution

    Here is a diagram: http://i.imgur.com/FfTwTD7.png
    So if the projected particle hits the hill at 90o then y/x=1/√3 and the velocity will be at 120o to the horizontal so y'/x'=-√3
    I solved these two equations simultaneously and I got θ=-60 but this looks wrong because it doesn't make sense.
    Please help :)
     
    Last edited: Apr 25, 2013
  2. jcsd
  3. Apr 25, 2013 #2

    tiny-tim

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    hi |mathematix|! :smile:
    shouldn't |y'| be larger than |x'| ? :confused:
     
  4. Apr 25, 2013 #3
    Yes, I fixed it :(
     
  5. Apr 25, 2013 #4

    tiny-tim

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    is your answer ok now? :confused:

    if not, show us your full working, so we can see what went wrong :smile:
     
  6. Apr 25, 2013 #5
    I did the working using the correct values but I got -60 degree for theta. I can't post the full solution now because it would take time and I have to study english now so I will re do it and see if I get a better answer.
    I basically substituted the equations of motion into y/x=1/√3 and y'/x'=-√3 and then solved them simultaneously, found theta and substituted back to find the time, is that the correct approach?
     
  7. Apr 25, 2013 #6

    tiny-tim

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    yes! :smile:
     
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