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Is this even solvable? Kinematics.

  1. Feb 18, 2014 #1
    1. The problem statement, all variables and given/known data

    A ball is thrown vertically upward from ground level with an initial velocity V0. The ball rises to a height, h, then lands on the roof of a building of height 1/2h. The entire motion requires 10s. Find the height, h, and the initial velocity, V0.

    2. Relevant equations


    3. The attempt at a solution

    I can't come up with anything, i'm using a final velocity of 0 m/s when running everything through and none of the values are making sense. I just need to know if it's actually solvable for real values. I'm in a hurry for work right now, but I will check back later.

    I'm using: t2: 10s
    t0= 0s
    v1= 0 m/s (turning point)
    a = -g
    y1= h
    y2= 1/2h
    v2= 0 m/s (stop)
    y0 = 0 m
  2. jcsd
  3. Feb 18, 2014 #2
    I think using that as your final velocity is your main problem so far. Yes, the final velocity will be zero once the ball hits the building and stops, but you can't use that value because the process of the object stopping isn't free-fall motion. You have to use the value of the velocity just before it lands as the final velocity.
  4. Feb 18, 2014 #3


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    You've just jotted down some trivial equations so far; you haven't actually written the proper kinematic equations involving distance as a function of time.

    Yes, there is a numerical solution for V0 and h, and there is a fair amount of algebra and logical deduction involved in obtaining it.
  5. Feb 18, 2014 #4
    [tex]s(t)=v_0t-1/2gt^2, s(t)_{\text{max}}=h=f(v_0,g),[/tex] solve [tex]s(t)=\frac{h}{2}[/tex] for t, and then plugin t=10s, get the larger answer
    Last edited: Feb 18, 2014
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