Question

The smoke from the gun barrel is seen 2 seconds before the explosion is heard. If the speed of sound in air is 340 ms⁻¹, calculate the distance of the observer from the gun. State the approximation used.

Answer 1

The light has a much larger speed (= 3 × 10⁸ ms⁻¹) in comparison to the sound (= 340 ms⁻¹), therefore we can assume that the light takes negligible time and the sound takes 2 seconds to reach the observer.
Now Speed = `"Distance travelled"/"Time taken"`
∴ Distance = Speed × Time
= 340 × 2
= 680 m.