posted by Steven .
For this problem, ignore air resistance.
You are to fire a rifle that shoots a particular bullet at 460 m/s at a target that is 45.7 m away and level with the rifle. Assuming that the acceleration due to gravity is 9.80 m/s², how high above the target must the barrel of the rifle be aimed such that the bullet hits the target?
* Physics - bobpursley, Wednesday, October 6, 2010 at 4:14pm
The real question is how far the bullet falls vertically during the trip.
how far does an object fall in that time?
h=1/2 g t^2
* Physics - Steven, Wednesday, October 6, 2010 at 4:57pm
That's not entirely correct... That would only be true if the rifle was fired horizontally, giving the x component 460 m/s towards the target.
However, that 460 m/s has some UPWARD y component too, reducing the x component by some amount...
* Physics - Damon, Wednesday, October 6, 2010 at 5:06pm
Forget that upward component. Too fast to be significant. look at 460 cos (angle up)
the cosine of your angle up will be essentially 1 and the sine will be about 0
* Physics - Steven, Wednesday, October 6, 2010 at 8:37pm
I would like to forget the upward component, as the object IS in fact a bullet fired at a fast velocity from a gun towards a target not too far away.
However, we're graded on the correctness of our problem solving. And, additionally, this factor WOULD become an issue if we were firing a marshmallow gun or a pea shooter at this distance, or if you were firing a sniper rifle at a target over a mile away.
We know, R=(u²sin2∆)/g ,∆=angle of projection
sin2∆≈1/460≈2∆ ,as ∆ is too small
So, tan∆≈∆ as ∆ is small