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Homework Help: Solving for 3 variables in projectile motion problem

  1. Feb 8, 2010 #1
    1. The problem statement, all variables and given/known data

    A dart is thrown at a 30 degree angle above the horizontal from a height of 1.6 meters. It hits the ground 20 meters away.

    a) find the initial speed?
    b)what is the maximum height reached by the dart (relation to the ground)?
    c)what is the speed of the dart as it hits the ground?

    2. Relevant equations

    y= y1 + Vy1t - 9.8t^2
    Vy = Vy1^2 - 2(9.8)(y - y1)
    Vy= Vy1 - 9.8t

    3. The attempt at a solution

    x1 = 20

    I understand that I most likely need to use the following three equations in order to isolate one variable. I am not sure which variable/how to.
  2. jcsd
  3. Feb 8, 2010 #2


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    Science Advisor
    Homework Helper

    Do you know what y1 (physically) means? Because its value is given in the problem.
    So is that of y.

    If you call the initial speed v, then you can rewrite v in terms of vx and vy and the angle (30 degrees).
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