a bullet is fired...?

Question

A rifle is aimed horizontally at a target 50.0 away. The bullet hits the target 2.70 below the aim point

what was the flight time in sec
and what was the velocity when it hit (m/s)

Answer 1

d(v) = (0.5) * g * t ^2

let d(v) = 2.7 and g = 9.8, solve for t. there's your flight time

d(h) = v * t

now let d(h) = 50, and t = the result from above. solve for v. congratulations, you've just done your own homework.

EDIT: Ratna, if you're going to give the poor kid the entire answer all without requiring any work on their part, you might want to make sure your answer is CORRECT first...

Answer 2

i'm assuming u mean "50.0 m away." in that case, you'll have to use the constant acceleration kinematic equations:
y=y0+vy0t+ayt*t/2, where y is the y-coordinate at a time t, y0 is the initial position (which we'll assume to be 2.70 m), vy0 is the initial velocity in the y direction (which is 0, since it's fired horizontally), ay is the acceleration in the y direction (which is -9.81 m/s/s, the acceleration due to gravity), and t is the time in seconds. Since the bullet goes 2.70 m downward, y is 0 at the end, so the equation becomes:
0=2.70-9.81t^2/2
2.70=9.81t^2/2
t^2=.550 s^s
t=.742 s, which is the flight time.
now, u must use the equation for velocity:
vy=vy0+ayt, where vy is the velocity in the y-direction. u know that vy0=0, so:
vy=0-9.81*.742
=-7.28 m/s, so when it hits, the bullet has a downward velocity of 7.28 m/s. now, u must find the velocity in the x-direction. u know there is no acceleration in the x-direction, so the x-velocity must stay constant. u also know that the bullet traveled 50.0 m in .742 s, so u can just use the equation:
vx=d/t
=50.0/.742
=67.4 m/s
the velocity of the bullet can now be given in vector notation:
v=<67.4 m/s, -7.28 m/s>
it can also be given in terms of speed and direction. to find the speed, you just use the pythagorean theorem on vx and vy:
s=sqrt(vx^2+vy^2)
=sqrt(67.4^2+(-7.28)^2)
=67.8 m/s
to find the direction, u must find the angle the velocity vector makes with the horizontal:
theta=arctan(vy/vx)
=arctan(-7.28/67.4)
=-6.16 degrees, or 354 degrees
when it hits, the bullet is moving at 67.8 m/s at 354 degrees.
t=.742 s, which is the flight time.

Answer 3

What the others just said

Answer 4

What promethius9594 said...

Answer 5

Good question CSI Miami will answer this tonight!