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Homework Help: Projectile motion flight time of ball

  1. Nov 18, 2007 #1
    [SOLVED] Projectile motion

    1. The problem statement, all variables and given/known data

    A ball is thrown with an intial velocity of v0 at an angle theta from the horizontal. Find the flight time of the ball in terms of H and g only.

    2. Relevant equations
    t = (2 v0 sin theta)/g

    3. The attempt at a solution

    Ok. I found theta to be the tan inverse of 4R/H. Thus, the initial velocity is sqrt[Rg/sin(2tan-1(4R/H))] - a little longwinded but accurate. However, my problem arises when I plug these values into the above equation and those really nasty 'R's refuse to go away, and the problem specifically states that g and H should be my only variables. I feel like i must be missing something really obvious, and if so, i apologise in advance, but please help anyway! Thank you!
  2. jcsd
  3. Nov 18, 2007 #2


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    Homework Helper

    When the ball reaches the height H, its velocity is equal to zero. So using kinametics equation we get (vosin theta)^2 = 2gH. From this equation find the value of (v0sin theta) and plug it the relevant equation.
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