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Homework Help: Freefall Problem

  1. Jan 17, 2008 #1
    I need help getting the base equations for a situation like this so I can complete all of the other problems on the page. Thanks ahead of time.

    1. The problem statement, all variables and given/known data
    A stone is thrown straight upward and it rises to a height of 20.0m. With what speed was it thrown?

    2. Relevant equations
    This is what I need.

    3. The attempt at a solution
    Answer: 19.8 m/s (given, the equations are what I need)
  2. jcsd
  3. Jan 17, 2008 #2


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    Homework Helper

    g is constant so the kinematic equations apply

    those are v=u+at;s=ut+1/2at^2;v^2=u^2+2as

    Where v=final speed,u=initial speed,a=acceleration,s=displacement
  4. Jan 18, 2008 #3

    Shooting Star

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    It's always very useful and time saving to use the symmetry in the rise and fall of an object. This means that in this case we have to calculate the speed after a fall of 20 m from rest. The eqn v^2 = 2gh gives it directly.
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