1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    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!

A Supersonic Waterfall?

  1. Jul 6, 2008 #1
    1. The problem statement, all variables and given/known data
    According to geologists, the water in a waterfall was supersonic, that is, it fell with speeds in excess of the speed of sound. Ignoring air resistance, what is the minimum height necessary to create a supersonic waterfall? (The speed of sound may be taken to be 340 m/s.)

    2. Relevant equations
    Treating water as particles, water falling down the fall is acted upon by gravity. Using the Newton's equation....I think??

    S = ut + 1/2 at^2

    3. The attempt at a solution

    S = ut + 1/2 at^2

    h = 340t + (9.8/2)t^2
    4.9t^2 +340t - h = 0. Solve the quadratic equation for t?

    But I have two variables...(h and t) so I don't know how to go any further...
  2. jcsd
  3. Jul 6, 2008 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    you need to use the veloctiy relationship

    [tex] v = v_0 + gt [/tex]

    to find the time required to reach 340 m/s then use that time in the distance relationship to find the distance.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook