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## #1 2006-10-22 13:29:22

eva0882
Member
Registered: 2006-10-22
Posts: 1

### trajectory

hi, i am not to bright and i was wondering if anyone could help me. i am doing a school project about trajectory. i have been trying to get all the formulas and everything but i just cant seem to get a good answer. i need to know if i shot a bullet at a 90 degree angle. how far will it go? i also need formulas about gravaty and pretty much everything that happens. thank you very much!:D

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## #2 2006-10-22 15:36:17

fgarb
Member
Registered: 2006-03-03
Posts: 89

### Re: trajectory

Sweet, I never got to shoot guns when I was in school.

You are asking some pretty broad questions though. What level of class is this? If you already know a little calculus that would make it a lot easier to explain some of this - you don't need to remember formulas then, you can figure them out yourself! But if not then that's ok too.

Whether you know calculus or not, the key is to not just know the formulas, you should try to really understand them. You're starting with a constant acceleration, g, from gravity. Acceleration is what changes velocity over time, so

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You start at some initial speed v sub i, and then over time gravity changes your speed more and more as you can see from the right most term. Of course, velocity changes position in the same way, but it's a little more complicated because the velocity isn't constant like acceleration is. Each of the terms should look reasonable though. What you get from a little calculus is:

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These two formulas can tell you all you need to know about the vertical movement of the projectile. As for the horizontal movement, as long as you can ignore air resistance it will always be going at the same speed. So as long as you treat the up and down movement of the projectile separately from the side to side movement you really only need to work with two formulas for most projectile problems.

But all formulas aside, it helps to clearly picture what you're dealing with (drawing a sketch helps).  All math aside, how far do you think a bullet would go if you shot it at 90 degrees (straight up)? This is a very broad topic so I'm going to stop here for now, but feel free to ask more specific questions.

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