Question

A boy aims a gun at a bird from a point, at a horizontal distance of 100 m. If the gun can impart a velocity of 500 ms^–1 to the bullet. At what height above the bird must he aim his gun in order to hit it (take g = 10 ms^–2)

• A. 20 cm
• B. 10 cm
• C. 50 cm
• D. 100 cm

Answer 1

Answer: (A)

20 cm

Answer 2

Time taken by bullet to travel a horizontal distance of 100 m is given by $\mathbf{t =}\frac{\mathbf{100}}{\mathbf{500}}\mathbf{=}\frac{\mathbf{1}}{\mathbf{5}}\mathbf{\sec}$

In this time the bullet also moves downward due to gravity its vertical displacement $h = \frac{1}{2}gt^{2} = \frac{1}{2} \times 10 \times \left( \frac{1}{5} \right)^{2} = 1/5m$= 20 cm

So bullet should be fired aiming 20 cm above the bird to hit it.