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Is there a simpler way to solve this free fall problem?

  1. Sep 12, 2007 #1
    [​IMG]

    1. The problem statement, all variables and given/known data
    (see scanned picture)


    2. Relevant equations
    kinematic equations of motion (*under condition that acceleration is constant)


    3. The attempt at a solution
    (see scanned picture)
    solved the problem......(please read further)

    i was just wondering if there is a more simpler way to attack this problem. only after an hour later (and constantly looking at the equations i can work with) did i have some weird flash of insight to do what i did and just jot things down on the paper until i arrived at the correct answer.

    the thing with free fall problems (or any physics problems for that matter) is that it is usually useless to "memorize" a method on solving a particular problem because not all the problems of a certain topic will be the same (i.e. different wording, certain conditions, etc.). that means, if i saw this problem a week later (assume that i did not think about this problem ever since) i would probably be confused and spend an hour again until i get that flash of insight, if at all. not sure if this is normal for you guys, but seems inefficient, especially when you have more homework problems to solve. i can only already see myself on a test day being like this.

    just to let you know, the problems in my book have a difficulty range of 1 dot to 3 dots. this was a 2 dot problem. (sad face)
     
  2. jcsd
  3. Sep 13, 2007 #2

    learningphysics

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    Homework Helper

    Hint: The displacement in the last second... is the displacement over t seconds (assuming t is the time it takes to fall) - displacement over the first (t-1) seconds.

    That gives you a way to find the time t of the fall... then you can get h.
     
  4. Sep 14, 2007 #3

    dynamicsolo

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    Homework Helper

    Because of the sort of information given in the problem, there isn't a good way to avoid needing to solve for the time; the "velocity-squared" equation won't tell you enough. learningphysics's hint is essentially what you need to do. But you can simplify the work by saying that after t seconds, (1/2)g(t^2) = (h-38) and that after one more second, (1/2)g([t+1]^2) = h . If you substitute the second equation into the first and multiply out the binomial-square, the (1/2)g(t^2) cancels out and you only need to solve a *linear* equation for t . Putting this value into your second equation then gives h.

    BTW, your answer is correct and this method will corroborate it.
     
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