Question

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

• A. $1\text{m}$
• B. $5\text{m}$
• C. $10\text{m}$
• D. $0.5\text{m}$

Answer 1

The correct option is B $5\text{m}$

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