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Homework Help: Catapult/Projectile Launcher Project - In Depth, Fairly Complicated - I'm stuck.

  1. Jun 9, 2012 #1
    1. The problem statement, all variables and given/known data
    I am required to make a projectile launcher of some form that will fire a golf ball a certain distance, a certain height through a window, and to have it land accurately on a target.

    -The device can only be 1x1x1 meter - no weight restrictions.
    -There will be two launches with 3 attempts each.
    -Launch 1 will have a 0.5x0.5 meter window located 2 meters away, and will be 2 meters high.
    -Launch 2 will have the same window, and the same height, but will be 4 meters away instead.
    -For each launch, the ball must pass through the window and then land at the target which is located 8 meters away.

    Here is a picture which helps describe a bit better: (to hell with 'not being able to include links'), type in i.imgur followed by .com and then /PKWAe.png

    I have been unable to solve this problem so far because it involves something I am building in real life. I will describe what I have below.

    I have done various calculations but they involve 'perfect' materials and such, which is impossible for me. I have determined, to my capability, that the ball must be launched at an angle of 17.51 degrees and a speed of 9.08m/s. But I had to make up a spring constant as I dont know what mine is for the elastic material I am using.

    2. Relevant equations

    Stuff to do with projectile motion. I've tried a few equations.

    2gy=0-Viy^2 height I must reach above launch location, 1.25m
    ax^2+bx+c=0 to get the time it will be in the air, 0.51s
    v=d/t to determine the X velocity of 15.68
    Tanθ=O/A to get launch angle
    Sinθ=O/H to get diagonal launch speed
    F=kx^2 to get my elastic constant K which ended up being 0.023
    F=ma to try and get F of 5.74N, to allow for rearranging of K.
    2as=vf^2 to get the acceleration per second of 124.92m/s

    3. The attempt at a solution

    I have made a projectile launcher : type in i.imgur followed by .com and then /RqRlp.png

    It consists of two vertical boards on a platform. They are hinged - allowing for adjustment of holes at various heights by moving the firing platform.

    The platform itself is a flat board with two pieces I cut at 45 degree angles for the ball to rest in. The ball will find its own center that way. The board itself can attach to different heights where holes have been drilled, and can pivot almost 90 degrees upwards.

    The ball is fired through the use of an elastic material which I was provided, it seems to be the inflatable lining from inside a bicycle tire, and once cut into thin strips should be elastic enough.

    I used all the equations I have listed to try and figure this out, but I am entirely stuck because...

    I cannot find out K for sure, V for sure, A for sure - all of which prevents me from the correct angle and height.

    I cannot figure out how to calculate firing from the elevated height. I decided that from 1m, in order to go above 2m and through the window, the ball must be fired to an elevation of 1.25m higher than the launch point, thus up to 2.25 meters.

    Once the ball reaches 8m after passing through the windows, that is the 8m which is still located 1m above the ground, and it would keep moving horizontally past 8m until finally hitting the ground 1m below.

    Honest to god, I'm awful at physics and my passing is relying heavily on this project being successful. I have until Tuesday to get it done, and have been trying to work on it here and there for two weeks but I have reached a road block. I cannot get the correct variables to fire it properly, and the teacher has been of zero help so far. I hope my post makes some semblance of sense and perhaps can help with others helping me out - because I am entirely stumped on what to do.

    If you need clarification on anything, just ask.
  2. jcsd
  3. Jun 9, 2012 #2
    All these views and no reply :(?
  4. Jun 10, 2012 #3
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