college physics

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using the quadratic equation on a 2 dimensional projectile motion problem...

i am solving for tf and i have it worked all the way down to:

-100m(tf)-100m(tf) / -10m/s^2(tf)^2
or
-200m(tf) / -10m/s^2(tf)^2

is the answer 20 seconds? algebra is not my strong suit =(

  • Need problem statement -

    What is the problem here. Is it something fired at some speed at some angle?

  • college physics -

    yes.. it's the "brothers of mercy" problem.

    a plane is flying at 40 m/s, descending at an angle of 37 degrees to the horizontal. it is 100 m in the air and it is trying to drop a package to a man at R distance. what is R?

    to find R, i needed to solve for time. that's where the quadratic came from

  • college physics -

    initial speed down = 40 sin 37
    = 24.1 m/s
    falls 100 meters, get speed down
    v = 24.1 + 9.8 t
    distance down
    100 = 24.1 T + 4.9 T^2
    4.9 T^2 + 24.1 T - 100 = 0
    T = 2.68 s
    now horizontal speed constant for 2.68 seconds
    d = (40cos37)2.68
    = 85.6 meters

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