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Homework Help: Velocity problem determining x and y components

  1. Sep 18, 2012 #1
    An object undergoing parabolic motion travels 100 m in the horizontal direction before returning to its initial height. If the object is thrown initially at a 30° angle, determine the x component and the y component of the initial velocity. (Neglect any effects due to air resistance.)

    I am not sure how to go about solving... I got an initial vector from the throw but I dont think it can be the initial velocity vector since I have no judgment of time.. could someone show me the process of solving this?
  2. jcsd
  3. Sep 18, 2012 #2


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    If we let "[itex]v_x[/itex]" and "[itex]v_y[/itex]" be the components of velocity in the x and y directions, respectively, then [itex]x= v_xt[/itex] and [itex]y= -4.9t^2+ v_yt[/itex] so we have [itex]y= -4.9t^2+ v_yt= 0[/itex] (the projectile hits the ground) and [itex]x= v_xt= 100[/itex] (the projectile hits the groud after 100 m). The fact that "the object is thrown initially at a 30° angle" means that [itex]v_y/v_x= tan(30)[/itex]. That gives you three equations to solve for the three values, t, [itex]v_x[/itex], and [itex]v_y[/itex].
  4. Sep 18, 2012 #3


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    If vsinθ is the y component of the velocity, what is the time the projectile takes to return to its Initial height?
    If vcosθ is the x component of the velocity, what is the expression for the range x?
  5. Sep 18, 2012 #4
    The time taken for the object to travel horizontally 10m is equal to the time taken from launching up and back to same level.

    It is a single body, at same place(different x and y coordinates) and at same time.
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