# Finding projectile speed

1. Feb 2, 2010

### lolomolo

I got an air gun and i need to find how fast (m/s) it fires a projectile. If i knew speed (s) the distance when it hits the ground (d) and the weight of projectile (10g) and the angle is horizontal zero degrees (0*) i know earth has a (9.8m/s) gravity pull so what els do i need to know and could you write me a formula to follow? Ty ; )

2. Feb 4, 2010

### cragar

you could do something simple like have a friend stand next to you and fire at a metal can like 100 meters away or 70 or what ever you can hit further the better , and count down to when you pull the trigger and then stop the watch when you hear the ping.
using s=d/t , and you might want to factor in the time lag for the ping at the speed of sound 343 m/s

3. Feb 4, 2010

### lolomolo

um easy? this thing shoots projectiles that blow holes in concrete slabs im sure "some friend" is going to stand there. meat shield much?

4. Feb 4, 2010

### lolomolo

and plus if i shoot only 100m im also going to find the impact force because im prety sure it shoots much farther

5. Feb 4, 2010

6. Feb 4, 2010

### cragar

ok I thought of another way . take a piece of foam board and place it 50 meters or so away , and aim at the top of the board then you can see where the bullet went through and you can measure this distance from the top and using d=1/2gt^2 you can calculate how much time it took the bullet to drop and then do s=d/t because you know the distance is 50 meters or how ever far you want to shoot it from , this may take some accurate shooting and a couple of trials but it should work.

Last edited: Feb 4, 2010
7. Feb 5, 2010

### lolomolo

thought of that but its not that accurate it shoots 2 in airsoft granade shells or AA bateries

8. Feb 5, 2010