Why is the efficiency of a rubber band slingshot constant

[CTHAEH]

Homework Statement

I need to explain for a lab, why the efficiency of a rubber band slingshot constant for different stretch lengths. I don't need math, just a general explanation of why kinetic energy of projectile/elastic potential energy in rubber band is constant.

Homework Equations

The Attempt at a Solution

I really couldn't think of anything. Please help

 

[haruspex]

Homework Statement

I need to explain for a lab, why the efficiency of a rubber band slingshot constant for different stretch lengths. I don't need math, just a general explanation of why kinetic energy of projectile/elastic potential energy in rubber band is constant.

Homework Equations

The Attempt at a Solution

I really couldn't think of anything. Please help

Not sure I can answer it either, in the sense of a reasonable basis for predicting that result.
But it might help to think about the two phases, stretching and releasing. If you were to plot the extension against tension during that cycle, what would you expect?

 

[CWatters]

Perhaps a slingshot is close to ideal? In which case the efficiency is always close to 100%?

 

[haruspex]

Perhaps a slingshot is close to ideal? In which case the efficiency is always close to 100%?

Possibly, but in that case one could look at loss, i.e. 1-efficiency, thereby exposing variation better.

 

[rcgldr]

The energy returned from stretched rubber is less than the energy used to stretch the rubber, known as hysteresis (the lost energy is converted into heat).

http://en.wikipedia.org/wiki/Hysteresis#Elastic_hysteresis