1. PF Contest - Win "Conquering the Physics GRE" book! Click Here to Enter
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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
    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

    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


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    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:)
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook