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Projectile motion

  1. Apr 4, 2010 #1
    An object is projected horizontally. After t seconds it has a horizontal displacement of 10cm and a vertical diplacement of 5cm.
    a) What is the value of t?
    b) What is the magnitude of the initial velocity?

    a) my attmept.
    :( Nothing Sorry i dont get it.
  2. jcsd
  3. Apr 5, 2010 #2
    First off, it can reasonably be assumed that we're talking about an object subject to 1 normal Earth gravity (g)?

    If so, this is relatively simple since it's only over a short distance span and you don't have to junk with changing gravity like with high altitude satellite launch problems.
    What you know:
    a (g=9.80m/s2)
    vi (0m/s)
    d (5cm down [-5cm])
    t (?)
    vf (?)

    1. Finding time span
    The four main kinematic equations use four variables usually with three known.
    We know a,vi and d with the intent of finding t, so let's use "d=vit+.5at2"
    Since vi equals "0" vertically, vit drops.
    Further algebra gets us "t=sqrt(2d/a)"
    Crunch your numbers.

    2. Finding initial horizontal velocity
    Gosh... if you need help here,--- .
    (By the way: "d=vt" TF "v=d/t")
    Last edited by a moderator: Apr 5, 2010
  4. Apr 26, 2010 #3
    Thanks, but I checked this like a month later, :D
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