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[111] Throw-up problem - Launch/freefall

  1. Sep 10, 2008 #1
    1. The problem statement, all variables and given/known data
    A stone is launched straight up by a slingshot. Its initial speed is 19.8 m/s and the stone is 1.40 m above the ground when launched. Assume g = 9.80 m/s2.
    (a) How high above the ground does the stone rise?
    wrong check mark m
    (b) How much time elapses before the stone hits the ground?

    2. Relevant equations
    D= Vot + (1/2)at^2
    V=at+Vo


    3. The attempt at a solution
    Vi=19.8m/s
    d=1.4m
    a=-9.8m/s

    I actually solved another question I had while typing it up on here.. maybe this one will be the same.

    Ok, I've attacked this thing every way I can think of, and my problem is the integration of it being launched from 1.4m above the ground. I tried 1.4=19.8t+ (1/2)(-9.8)t^2, solving quadratically for t=3.9688 and t=.071987, neither of which are correct. I know finding the time is the key to the solution, but im not sure how to integrate the 1.4m into the formula.

    Can someone point me in the right direction?
     
  2. jcsd
  3. Sep 10, 2008 #2
    Let me rewrite this your formula for part A is y= (v^2-v0^2)/(2a).

    After you get your y component your formula for Par B is: t= v-v0/a.

    t = time
    a = acceleration
    y = distance (vertical)

    And that should give you the answer for the problem.

    Sorry went through 3 or so edits kept copying the wrong equation, that should be it thou. Times the answer by 2 to get the up time and downtime for Part B.
     
    Last edited: Sep 10, 2008
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