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!

Ball from a cliff

  1. Jul 27, 2009 #1
    A girl at the bottom of a [tex]100\ m[/tex] high cliff throws a tennis ball vertically upwards. A boy at the very top of the cliff drops a golf ball so that it hits the tennis ball while both balls are still in the air. The acceleration of both balls can be assumed to be [tex]10ms^{-2}[/tex] downwards.

    With what speed is the tennis ball thrown so that the golf ball strikes it at the top of its path?

    I don't know where to start with this one. Is the question missing something? I assume that both balls were both released at the same time...

    Any help would be great.

  2. jcsd
  3. Jul 27, 2009 #2
    for the tennis ball: v = vi + at
    0 = vi -10t
    (1) write an equation with t = ....

    for the golf ball: d=vi x t + (at^2)/2
    vi = 0 (for the golf ball) a = 10 and substitute the t from equation (1)

    you'll end up with (2) d = ....

    for the tennis ball: 100 - d = vi x t + (at^2)/2
    a = -10, substite equation (2) for d, and substitute (1) for t

    gudluck and tell me waht the answer is
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook