1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Catapult Project Need Help Please

  1. Dec 18, 2014 #1
    I'm doing a catapult project but I'm sort of confused.
    I need to find the spring constant in order to get the elastic potential energy.
    The force of pulling back the catapult lever to 36 degrees above the horizontal is 4.2 N. Right before the lever is at rest, 90 degrees, the force is 1.4 N.
    One of my lab partners got the force average as 6.68 N.
    My teacher told me to use the arc length as the x in the equation.
    When that was plugged in to the equation I got 68.346 N/m as the spring constant. Does that make sense? I asked another group and they got a spring constant of about 2 N/m.

    I know I am suppose to use Hooke's Law but am I suppose to use the average force or the difference of the forces?

    What am I doing wrong?
    Last edited: Dec 18, 2014
  2. jcsd
  3. Dec 18, 2014 #2


    User Avatar
    2017 Award

    Staff: Mentor

    Without a sketch and other additional information, I think it is impossible to tell.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook