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Homework Help: Projectile motion (magnitude and direction)

  1. Feb 3, 2009 #1
    1. The problem statement, all variables and given/known data
    A projectile is fired at a speed of 45 m/s at an angle of 40 degrees above horizontal. Determine the magnitude and direction of its velocity 4 seconds later.

    2. Relevant equations
    ax=0 ay=-g

    3. The attempt at a solution
  2. jcsd
  3. Feb 3, 2009 #2
    find the vy and the vx after 4 seconds and find the resultant vector.
  4. Feb 3, 2009 #3
    yeah i dont get how to do that though
  5. Feb 3, 2009 #4
    oh hahah ok well
    Given: vi= 45 m/s and t = 4
    so vyi = sin (40) vi and vxi = cos (40) vi

    and to find the speed in four seconds you use the kinematics equation
    vyf = vyi + (ay) (t) and velocity in the horizontal remains constant since ax = 0

    find those to values and vf = sqrt ( vyf^2 + vxf ^2)

    Do you understand it? if not I'll try to explain it a bit more
  6. Feb 4, 2009 #5
    yeah i got it thanks
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