Question

The initial speed of a bullet fired from a rifle is 630 m/s. The rifle is fired at the centre of a target 700 m away at the same level as the target. How far above the centre of the target the rifle must be aimed in order to hit the target?

Options

• 1.0 m

• 4.2 m

• 6.1 m

• 9.8 m

Answer 1

6.1 m

Explanation:

Let t represent the amount of time it took the bullet to hit the target.

∴ 700 m = 630ms^-1 t

⇒ t = `(700"m")/(630"ms"^-1) = 10/9`sec

For vertical motion, 

Here, u = 0

∴ h = `1/2"gt"^2=1/2xx10xx(10/9)^2`

= `500/81`m 

= 6.1 m

Hence, In order to hit the target, the rifle must be pointed 6.1 m above the target's centre.