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Homework Help: Multivariable Motion in Space

  1. Sep 21, 2009 #1
    1. A medieval city has the shape of a square and is protected by walls with length 550 m and height 16 m. You are the commander of an attacking army and the closest you can get to the wall is 100 m. Your plan is to set fire to the city by catapulting heated rocks over the wall (with an initial speed of 80 m/s). At what range of angles should you tell your men to set the catapult? (Assume the path of the rocks is perpendicular to the wall. Round the answer to one decimal place. g ≈ 9.8 m/s2)

    2. Nada clue other than some kinematics and vectors

    3. Tried using kinematics but failed miserably. Help! C'mon it's about medieval stuff! ;)
  2. jcsd
  3. Sep 21, 2009 #2


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    I guess that means the walls are 550m on each side. Could be total length I suppose but that isn't clear. Anyway you have the distance from the wall

    (see attachment for picture)

    So I guess you aim it high enough so it just clears the the top of the first wall on the way down, and low enough so it arches over the first wall to the foot of the second wall -- if you can. So set up your equations of motion and get cracking. :-)

    Attached Files:

    Last edited: Sep 21, 2009
  4. Sep 21, 2009 #3


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    Your minimum angle would be where max height of the trajectory = 16m, because your projectile has to get over the wall. Maximum would be range = 100m to throw the projectile past the wall.
  5. Sep 21, 2009 #4
    Ya LCKurtz is right, you dont seem to now where to start so...

    Your at 100 m of the first wall and 650 m of the second you now the highest altitude will be half-way 325m and... It's your homework. :-p
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