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Homework Help: Projectile Motion

  1. Apr 22, 2008 #1
    Scott kicked a football with an initial velocity of 50 ft/sec at an angle of 65 degrees with the horizontal and at a height of 3 feet. Write the equations that would model this situation and answer the following:

    x(t) = _____________ (fill in formula with variable values plugged in)
    y(t) = _____________ (fill in formula with variable values plugged in)

    b) What is the max height of the ball?
    c) How far did the ball land from Scott?
    d) How long was the ball in the air?

    Calculator problem if that wasn't obvious enough.


    x(t) = (V * cos x)t
    y(t) = -0.5gt^2 + (V * sin x)t + h

    My attempts: (which are wrong by the way)

    x(t) = (50 * cos 65)t [CORRECT]
    y(t) = -0.5(9.8)t^2 + (50 * sin 65)t + 3 [ITALICIZED PART IS WRONG; I figured g stood for gravity, so 9.8, right?]

    107.694 ft (didn't get formula right, and probably didn't use calculator correctly, so these are probably far off)

    190.178 ft.

    Didn't have enough time to finish.

    This is a pretty quick PreCalc problem if you know what you're doing (which I didn't), so it would really help if one could do this.

    And if one could tell me what mode settings my TI-83 should be on when I do this, I'd appreciate it.

    And I apologize; in my 1AM rush to figure this problem out so I don't get another 10 points off on another test, I posted this in the wrong forum.
    Last edited: Apr 22, 2008
  2. jcsd
  3. Apr 23, 2008 #2


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    You were right in thinking that g stood for gravity, it simply is a matter of units. 9.8 represents the acceleration in m/s^2, whereas you're working with feet in this problem!
  4. Apr 23, 2008 #3
    Bah, so what would the correct # be?
  5. Apr 23, 2008 #4
    32 right?
  6. Apr 23, 2008 #5


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  7. Apr 23, 2008 #6
    Thank you very much. My test grades will finally get the justice they deserve.
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