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Homework Help: Max height

  1. Jun 14, 2010 #1
    1. The problem statement, all variables and given/known data
    A projectile is fired across a horizontal flat plane. Its initial velocity is 25.5 m/s and is fired at an angle of 31.8° above the horizontal

    (a) How long does it take to get to the maximum height?
    (b) What is the maximum height?
    (c) Determine the horizontal and vertical components of the velocity vector at the maximum height.
    (d) Determine the horizontal and vertical components of the acceleration vector at the maximum height.

    2. Relevant equations
    I think a we use Vx = Vox + axt = 0 = 25.5m/s + (-9.8m/s^2)t = -25.5m/s/-9.8m/s^2 = t = 2.6sec
    I think on b. we use y = v^2-V^2o/2a = 0-(25.5m/s)^2/2(-9.8m/s^2) = 33.18m
    c and d I am stuck
    3. The attempt at a solution
  2. jcsd
  3. Jun 14, 2010 #2
    The only problem with using the horizontal equation to find time is there will be no accel in that direction,(unless friction is taken into account but it did not say in your problem) so your time variable will disappear. Gravity is only accelerating in the y direction, which also has a time variable. You also need to break apart your velocity into it's components, that is, how much is contributed to the y direction and how much is contributed in the x direction. You can use trig to solve for that. See how that helps.

    Last edited: Jun 14, 2010
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