# Homework Help: Help in calculating efficiency of a catapult

1. Apr 18, 2010

### pcgmks

Help with a catapult

1. The problem statement, all variables and given/known data
Hi all I have design a prac to investigate the efficiency of a catapult, was wondering if anyone could shed some light into this area

2. Relevant equations

Ee=0.5kx^2 (hookes law)

3. The attempt at a solution

I was thinking that my independent variable for the experiment is to change the length of the catapult arm thus changing the distance (x) in which the rubber band is stretched each time, while the dependent is how far the projectile is launched, from this can i determine the efficiency of the catapult?
was thinking that i collect how far the weight is projected each time- from the same angle of 45*? - then do i then need a formula to find out the force used and then compare to potential elastic energy?
so i am not sure how to piece this together fully from here
was told efficiency = output work/energy used, but what does that mean exactly and would it be helpful in this situation,

if anyone could help, it would be much appreciated,
thanks

Last edited: Apr 19, 2010