Question

A rifle shoots a bullet from the ground level with a muzzle velocity of $400m/s$ at a small target $400m$ away on the ground. The height above the target at which the bullet must be aimed to hit the target is
$(g=10m{s}^{-2})$

• A. $1m$
• B. $5m$
• C. $10m$
• D. $0.5m$

Answer 1

The correct option is B $5m$

Let the height above the target at which the bullet must be aimed $=H$
According to question
$R=400m$
$\Rightarrow 400=u\times t$ .....(i)
Time taken by the bullet to reach the ground $=\sqrt{\frac{2H}{g}}$
From eqn (i),
$400=u\sqrt{\frac{2H}{g}}400=400\sqrt{\frac{2\times H}{10}}\Rightarrow H=5m$