Question

The radiowaves travel at a speed of 3 × 10⁸ ms⁻¹. If a radar can hear an echo from an enemy plane in 0.015 milliseconds, how far is the enemy plane from the radar?

Answer 1

Given t = 0.015 millisecond = 0.015 × 10⁻³ s; v = 3 × 10⁸ ms⁻¹

\[ \text{Now, velocity of radio waves} = \frac{2d}{t} \]

\[ \therefore \ 3 \times 10^{8} \ \mathrm{ms^{-1}} = \frac{2 \times d}{0.015 \times 10^{-3} \ \text{s}} \]

\[ \therefore \ d = \frac{3 \times 10^{8} \times 0.015 \times 10^{-3}}{2} \ \text{m}\]

∴ d = 2250 m

∴ d = 2.250 km