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Homework Help: 2D Motion with a missle/engines

  1. Oct 5, 2008 #1
    On a spacecraft two engines fire for a time of 505 s. One gives the craft an acceleration in the x direction of ax = 5.10 m/s2, while the other produces an acceleration in the y direction of ay = 7.30 m/s2. At the end of the firing period, the craft has velocity components of vx = 3610 m/s and vy = 4928 m/s. Find the magnitude and direction of the initial velocity. Express the direction as an angle with respect to the +x axis.

    Vf= Vi +at

    tan O= opp/adj

    3610 m/s = Vi + (5.1 x 505)

    Vi= 1034.5 m/s

    tan O= 7.3/ 5.1
    O= 55.06 degrees

    the answer was incorrrect and I have no idea what else to do
  2. jcsd
  3. Oct 6, 2008 #2


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    Staff Emeritus
    Science Advisor
    Gold Member

    You found the initial x component well enough but you didn't find the y component. You then need to find the magnitude (i.e. pythagoras) and then apply your tan formula to the initial speeds.
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