Investigating Unexpected Results in Elementary Experiment

[nomadreid]

You mean (v2*sin2A)/g.

oops, yes. Apologies, .

Also, it looks like at release the projectile is about 2.7cm above the ground, which should add about 5cm to the range.
Feeding 111cm into the formula I get 3.7m/s.

OK, that makes a lot more sense now. Thanks very much, haruspex.

Ok, so this is where the actual geometry of the slingshot could come into play.

Thanks again, erobz. I presume it is OK for me to use your diagram (but with numbers, since an equation with that many variables is a bit much for a 13-year old) in explaining some of these ideas in my next lesson with the student?