How to calculate the efficiency of a trebuchet?

[physical..O.o]

Homework Statement

Hi, VERY URGENT and I am so confused

Find the efficiency of the optimum trebuchet.

Optimum trebuchet Specs:
Counterweight= 5kg
Sling Length= 78cm (laid out fully)
Length from fulcrum to load= 44cm
Length from fulcrum to counterweight=16cm
Height the weight drops when fired = 29.632cm
Average range = 23.7733
Weight of projectile = 46g
Gravity = -9.8

Homework Equations

KE= 1/2 mv^2 (no idea what to use this for and when, apparently we needed to, this is why i am so confused. what has it got to do with this?)

Actual measured range/ (2*(counterweight mass*distance the counterweight falls)/mass of projectile)

(Force(load)*Distance (load))/( Force(effort)*Distance(effort))

F=Ma

The Attempt at a Solution

23.7733/ (2*(5*0.29632)/0.046)
= 0.369*100
= 36.9%

OR

(0.046*-9.8*0.44)/(5*-9.8*0.16)
=0.0253
=2.53 %

im so confused

 

[physical..O.o]

Homework Equations

KE= 1/2 mv^2 (no idea what to use this for and when, apparently we needed to, this is why i am so confused. what has it got to do with this?)

Actual measured range/ (2*(counterweight mass*distance the counterweight falls)/mass of projectile)

(Force(load)*Distance (load))/( Force(effort)*Distance(effort))

F=Ma

another equation i missed

GPE= mass of counterweight*gravity* distance weight falls