Question

A bullet is fired from the gun with a speed of 1000 $ms^{ -1}$ in order to hit a target s = 100 m away. At what height above the target should by gun be aimed? (The resistance of air is neglegible and g = 10 $ ms^{ - 2}$

• A. 23 m
• B. 15 cm
• C. 9 cm
• D. 5 cm

Answer 1

Answer: (D)

The time taken to cover the horizontal distance of 100 m from the gun to the target is given by
t = $ \frac{ 100 }{ 1000 } = 0.1 s $
During this time, the bullet will fall down vertically under gravity.
Hence, height h = ut + $ \frac{ 1}{2} gt^2 $
= 0 + $ \frac{ 1}{2} \times 10 \times (0.1)^2 $
= 5 $ \times 0.01 = 0.05 \, m = $ 5 cm