# How can you make it go a certain distance?

1. Jan 12, 2013

### mizz_melanie

We have to build catapults in school and the teacher wants us to hit targets placed 2-4 meters but to get it to go a certain distance (2.2) How can I do it mathematically (with protectors or measuring length)? What formulas can I use?

- Also the targets will be randomly placed the day i have to shoot it

2. Jan 12, 2013

### Bobbywhy

mizz melanie,

Google is your friend. It can help you find information. Learn to use Google search and you will get new knowledge, satisfaction, and be happier. I entered the search words “calculate distance of projectile” and in 0.49 seconds about 1,140,000 results appeared. Below please find three that you may find useful:

How to Calculate the Distance of a Projectile
http://www.ehow.com/how_6357145_calculate-distance-projectile.html#ixzz2HoYg1DQI

http://en.wikipedia.org/wiki/Trajectory_of_a_projectile

http://www.calctool.org/CALC/phys/newtonian/projectile

Let us know how your project goes. (edit) If you have any doubts or further questions, post them here. Members here are always willing to assist any true searcher for the behaviours found in our natural world.

Cheers,
Bobbywhy

3. Jan 13, 2013

### CWatters

melanie - Have you covered the standard equations of motion yet? I mean equation such as V2=U2 + 2as.

If not then this is probably an experimental exercise. Set up the catapult so it fires the projectile at a fixed angle (say 45 degrees). Then arrange so you can stretch the catapult a controlled amount. Fire off numerous shots with various amounts of initial stretch. Plot a graph for stretch vs distance. Try and get lots of data that covers the likely range (eg 2 - 4m). Then when the teacher tells you the target distance you can look up the stretch required. I suspect it won't be possible to get accurate results. Slight changes to the angle may make a big difference.

If you are familiar with the standard equations then the distance will depend on the initial launch velocity and launch angle. See links Bobbywhy posted. The launch velocity will depend on the properties of the elastic used in the catapult (Google Hookes law).