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Homework Help: Using projectiles to solve for 2-D motion problems

  1. Sep 25, 2010 #1
    1. A landscape architect is planning an artificial water fall in a city park. Water flowing at 1.56 m/s will leave the end of a horizontal channel at the top of a vertical wall 2.01 m high and from there fall into a pool.
    (a) How wide a space will this leave for a walkway at the foot of the wall under the waterfall?
    (b) To sell her plan to the city council, the architect wants to build a model to standard scale, one-twelfth actual size. How fast should the water in the channel flow in the model?




    2. s=v(initial)*t + 1/2*at^2



    3. Okay, so I was able to get part A by calculating horizontal and vertical motion.
    vertical motion:
    s=v(initial)*t + 1/2*at^2
    -2.01=1/2*(-9.8m/s^2)*t^2
    t^2= .410
    t=.64 seconds

    then, I plugged the time in to this equation for horizontal displacement:
    s=(1.56m/s)t + 0*t^2
    s=(1.56m/s)(.64s)
    s=.999m=1m

    Part B is what I cannot figure out.
    I tried dividing the initial velocity of 1.56m/s by 12, but I got the wrong answer of .13m/s.

    If you can please give me a hint about how I'm supposed to solve for part B, I'd really appreciate it! :D
     
    Last edited: Sep 25, 2010
  2. jcsd
  3. Sep 25, 2010 #2

    fzero

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    For part B you need to rescale the vertical displacement to match the model and find the new time for free-fall. The velocity can be found from the equation for the rescaled horizontal displacement.
     
  4. Sep 25, 2010 #3
    thanks so much! I just went back and figured out the answer:)
     
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