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# Basic SUVAT stuff

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1. A bullet is fired horizontally at a speed of 200m/s at a target which is 100m away. Ignoring air resistance calculate how far the bullet has fallen when it hits the target.

I used
average v=s/t
200=100/t
200t=100
t=100/200
t=0.5s

then I said gravity was 9.81m/s/s and so i did
t*gravity = distance travelled down
0.5*9.81= 4.905m

The answers said it was 1.2m travelled down. How do you get there?

2. Where do you get your t*gravity = distance from

s=ut +0.5at^2
3. ooh i did t*gravity because i thought gravity = distance travelled down

thanks : ) i forgot about the equations :/ Silly me.
4. t*gravity =/= distance

t*a (=t*g) would be the increase in speed (or the final speed in this case, as the initial vertical speed is 0). This can be seen just by looking at units:

Units of (t*a) = Units of t * units of a = s * m/s^2 = m/s. This is a unit of velocity.

TenOfThem (post 2) gives you the right equation to use.

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Updated: October 28, 2011
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