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Homework Help: Horizontally Launched Projectiles

  1. Jan 15, 2012 #1
    1. The problem statement, all variables and given/known data
    An airplane loaded with flame retardant travels horizontally at 200. km/h. The altimeter indicates that the plane is 180. m above the ground. The pilot wants to know how far in advance of the fire to release the retardant. Please assist her.
    The answer was given, which is 336 meters

    2. Relevant equations

    3. The attempt at a solution
    So I plugged in all the numbers, 180 for d, 0 for vi, -9.81 for a. I got to 180=4.905t^2, which turns to 36.69. Then, I squared it, and got about 6.8, which is nowhere close to the time I need, which is 1.68. Please help me!
  2. jcsd
  3. Jan 15, 2012 #2
    This problem is similar to firing a bullet horizontally with velocity of 200m/s and an altitude of 180m and asking how far it will travel. In the equation you used the initial velocity in the vertical direction is zero but I think you substituted the initial horizontal velocity.

    See horizontal projectile motion,

    http://www.mrfizix.com/home/projectilemotion.htm [Broken]



    Good luck.
    Last edited by a moderator: May 5, 2017
  4. Jan 15, 2012 #3
    By Vi, I meant ViY. I don't understand what I did wrong from the pages you sent me to. I know I'm doing something way wrong, I'm just not sure what
  5. Jan 15, 2012 #4
    OK, your time looks right, so the distance should be t*200m/s which is much larger then the "right" answer. One of the numbers in your first post are wrong?
  6. Jan 15, 2012 #5
    Yeah probably, I found these problems online, so they may be a bit messed up :mad:
  7. Jan 15, 2012 #6
    Check your units. The problem specifies the horizontal velocity to be 200 km/h, not 200 m/s.
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