Help Design a Catapult to Hit Specific Targets

[DeathEater]

Homework Statement

For my physics class, I have to design a catapult with specific requirements. The launch angle (in reference to the ground) has to be adjustable, it has to hit specific targets within a range of 3-15 feet (the targets can only be at even distances, so only 4 ft, 6 ft, 14 ft etc.), and the initial velocity of each launch has to be the same.

Homework Equations

Before anyone asks, yes I have looked up possible designs already, but none consider initial velocity when talking about the adjustable angles. Most designs just say to have an adjustable bar to move up an down in order to change the angle it's launched from. However, the launch velocities that result from that design are varying.

The Attempt at a Solution

I proposed to have a standard catapult on a base that itself is adjustable so that the angle may change without the initial velocity changing in a drastic way. I was then going to employ a use of hooks along an arm to attach a large rubber band or bungee cord to so that the launch distance can change.

Would this design work well? what adjustments could I make to improve it, or are there better ideas you might have?

 

[jedishrfu]

Can you draw a picture with labels and explain how it might work?