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Homework Help: Need help with spring launcher please

  1. May 24, 2008 #1
    1. The problem statement, all variables and given/known data
    hi this is my first time posting here but i'm been on the forum alot just looking for help on this assignment I have

    I need to make a spring laucher thats able to change angles and distance
    heres an example of my lancher

    A spring is launched to a box The target is at a certain distance and height. The question is how do I find the amount I need to strech the spring to get it into the air. bonus how do I add air friction to the equation becaue it obviously makes a diffence

    2. Relevant equations
    heres given
    my spring constant
    distance between spring and box
    hight of box
    angle since its determine by the user




    3. The attempt at a solution

    no idea how to solve this
  2. jcsd
  3. May 24, 2008 #2
    nm about the picture I cant post a image untill I have 15 posts but its simply an L shaped design with a protractor on its side and a ruler on the top where the spring is lanched
  4. May 24, 2008 #3
    This may help: Use the formulas for the amount of potential energy in the spring at a certain distance, then equate that with the kinetic energy of the spring once it has left, this will give you the velocity related to the stretch in the spring.
  5. May 24, 2008 #4


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    Science Advisor
    Homework Helper

    Welcome to PF!

    Hi psp101! Welcome to PF! :smile:
    No … you mean y = v0sin0t - 1/2gt^2.

    And you need to find the other value of t (other than 0, that is) for which y = 0.

    Then you can use the x formula. :smile:

    Is this a practical experiment, so you have to make a real launcher?

    If so, how are you going to get the spring to go straight?

    Springs are meant to be bendy, and they'll bend sideways as well as up-and-down.

    Won't you need something like a long tube?

    As to air resistance, I would expect a spring would be horribly un-aerodynamic.

    They don't build aeroplanes spring-shaped, do they (oh … except maybe the Boing … 911! :biggrin: )?
  6. May 25, 2008 #5
    lol thanks for the help actually the spring is very straght all I need to do is strech it a certian amount with the ruler to meause it to get it across a distance.the only problem before was that I did'nt know how to find that amount I need to strech it to.

    I already built the design but I noice the equation is slighty off I just guessed its because of air friction.
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