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Efficiency projectile

  1. Apr 18, 2010 #1
    Independent variable and spring constant k

    Hi all,
    If someone could spare a minute to help answer my question I would appreciate it greatly,

    I am trying to design an experiment to investigate the efficiency of a catapult,
    But need help in what i should use as the independent variable-
    and how i should use the spring constant k ( get a spring with a known constant k or change the constant each time)

    I am using a Catapult- a standard weight- and will to measure distance of projectile.
    find the kinetic energy- divide it by the Potential energy to get % efficiency,

    2. Relevant equations

    Elastic Potential Energy Ee=0.5kx^2 (hookes law)
    Kinetic Energy Ek= 0.5mv^2 (v=d/t)

    To find the Energy efficiency = Ek/Ee x100

    3. The attempt at a solution

    Need to clarify what i need to change each time to get a range of data,
    Would the independent variable - being the length of the catapult arm work (is this the same as how far the spring or rubber band is stretched -the x in elastic pot. formula -) ?
    or do I change something to do with the Elastic energy properties like the constant k?

    the the dependent variable is how far the projectile is launched. and was thinking that i collect how far the weight is projected each time- from the same angle of 45*?

    if anyone could help soon, it would be much appreciated,
    Last edited: Apr 19, 2010
  2. jcsd
  3. Apr 19, 2010 #2
    Would it be easier if i had a spring with a known spring constant k and change the arm length each time,
    ( i know that a larger arm will make it go further but has it got to do with torque or is it irrelevant to this experiment),
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