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Homework Help: 2D Motion (Projectile)

  1. Mar 9, 2013 #1
    1. The problem statement, all variables and given/known data
    A ball is kicked with initial velocity 40 m/s at an angle of 37 degree above the horizontal. What is the time (in seconds) needed to reach the maximum height?

    2. Relevant equations
    h= Voy t - 0.5 g t^2
    Vy= Voy - g t
    Vy^2= Voy^2 - 2 g h

    d= Vox t
    Vx= Vox

    3. The attempt at a solution
    I reached to a point where I couldn't figure out a way to continue..

    I used this equation
    h= Voy t - 0.5 g t^2
    h= (40 sin(37)) t - 5 t^2

    I have 2 unknowns..
    I tried to use Vy=Voy - g t
    to find the time, I got so far these 2 equations
    h= (40 sin(37)) t - 5 t^2
    0=(40 sin(37)) - 10 t

    Is this right?
  2. jcsd
  3. Mar 9, 2013 #2
    Yes, you can use either one to solve for t. If you use the upper formula, remember that you get the total flight time which you have to divide by 2 since we assume the projectile is symmetric.
  4. Mar 9, 2013 #3
    Thank you, I used the second equation and the answer is 2.4 s.. is it right?
  5. Mar 9, 2013 #4
    Looks good.
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