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Homework Help: Very simple gravity/time/distance travelled problem

  1. Dec 8, 2009 #1
    1. The problem statement, all variables and given/known data
    This isn't really homework, because I'm not at school anymore (aged 42!) but I will describe as best as I can.

    A small object like a droplet of water is released from a height (point A), falling on the surface (Point B) with initial speed 0. Distance between A and B, I will call d and obviously there's gravity (g) and time it takes for the droplet to fall from A to B, I will call t1. I know the equation so that given d is known, and so is gravity, then I can calculate time (t1).

    Suppose that between points A and B, there's a point X. By the time the droplet has reached X is already has a certain speed. How do I calculate the time (t2) that it takes for the droplet to travel from X to the surface (B)?

    2. Relevant equations

    t1=square_root((2 * d)/g)

    3. The attempt at a solution

    I know (or at least I think I know) that I can't use the same equation to calculate t2 because the droplet already has a certain speed.

    Apologies, if I'm not explaining this very well. I've not done any physics for 25 years and the reason I need this is because I'm doing high speed photography with falling objects.


  2. jcsd
  3. Dec 8, 2009 #2
    If you know the distance AX, you can use the above equation to calculate the time for the droplet to reach point X, t[X]. As t[1] stays the same whether or not you add an extra reference point, simply substract t[X] from t[1] and you have your answer.

    Hope this helps.
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