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Homework Help: Ball launched at an angle

  1. Mar 24, 2010 #1
    1. The problem statement, all variables and given/known data

    A ball is launched from the origin at an angle of inclination of 50 degrees above the xy plane. If the ball lands at coordinates (4,7,0), find the initial velocity of the ball.


    2. Relevant equations
    x=(voCos(50)Cos(theta))t
    y=(voCos(50)Sin(theta))t



    3. The attempt at a solution
    Unfortunately, I have the answer, but I am unaware of how it was obtained.

    x=.3189vot
    y=.5581vot

    z=vosin(50)t-4.9t^2

    z=0 when t=.1563

    so vo=sqrt(4/(.3189)(.1563)) = 8.957m/s

    Can anyone give me some insight as to how the x and y was solved for?
     
    Last edited: Mar 24, 2010
  2. jcsd
  3. Mar 24, 2010 #2

    rl.bhat

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    Homework Helper

    Hi Michels10, welcome to PF.
    x= vo*cosθ*t. So t = x/vo*cosθ...(1)
    y = vo*sinθ*t - 1/2*g*t^2.......(2)
    x and y is given. Angle of projection is given.
    Substitute the value of t in eq.(2) and solve for vo
     
  4. Mar 24, 2010 #3
    Hi, thank you for the response!

    I made an effort to plug in t and I did not receive the correct answer.

    7=vo*sin(50)(4/(vo*cos(50)))-(1/2)*(9.8)*((4/(Vo*cos(50)))^2

    does this look correct?

    I plugged it into wolfram and ended up with a result of +-(9.21823 i)
     
  5. Mar 24, 2010 #4

    rl.bhat

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    Homework Helper

    an angle of inclination of 50 degrees above the xy plane
    The above statement indicates that the angle is above the xy plane, and the ball lands on the xy plane at the co-ordinates (4, 7, 0). So here y = 0 and x = sqrt(4^2 + 7^2).
    Now try to solve the problem.
     
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