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Homework Help: Vertical displacement

  1. Jun 4, 2006 #1
    I have my physics exams on Friday so was just revising some of the stuff I covered earlier in the year. I got this question:

    "A ball is thrown vertically upwards with a speed 10ms^-1 from a point 2m above horizontal ground. Calculate the length of time for which the ball is 3m or more above the ground."

    I did end up getting the correct answer of 1.83s, but I took an extremely long-winded route. I calculated the total time the ball would be in flight, then subtracted the initial part under 3m and the final part under 3m, which I calculated using the simple equations of motion.

    I seem to remember earlier on in the year using a much easier and quicker method to get the answer, but I have forgotten it, and can't seem to find it in my notes. How would you go about solving this question?
    Last edited: Jun 4, 2006
  2. jcsd
  3. Jun 4, 2006 #2
    [tex] y = y_{0} + v_{y0}t + \frac{1}{2}at^2 [/tex]

    is the general kinematic equation you want to use,
    where in your case:

    solve the resulting quadratic equation for t
    Last edited: Jun 4, 2006
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