projectile projects

must it go up or along the horizontal? You could make one of those rockets with the water in and pump it with a bicycle pump. you would need a capsule in which to hold the tomato but that wouldn't be difficult. You have to have a drinks bottle for your rocket. I'm sure you can find lots of instructions for making them online. Or you could have a javelin type missile where you make a long holder and put your tomato on the end, then use a leather strap to help you to fling it further than an arm alone can throw it(much longer reach because of the strap).

You could also try a catapult or ballista. At my old school we had a competition where you would build a catapult or ballista and see how far you could throw/shoot an object. It may work for tomatoes too.

If you are not allowed to use any chemical propellants such as powders then I suggest that you should go with the old ways. Use a very strong spring, it must be a very large spring so as to satisfy the strength of throwing your tomato at a very far distance. Another suggestion is that you can use some rubber bands, it must be a a thick rubber that you can stretch but I think it's not as strong as the spring.