A car is moving with a speed of $72 {km}/{h}$ towards a hill. Car blows horn at a distance of $1800 m$ from the hill. If echo is heard after $10 s$, the speed of sound (in ${m}/{s}$) is

The car is traveling at 72 kmph, which converts to 20 m/s. The horn is sounded 1800 m from the hill, and the echo is heard after 10 s, during which the car moves 20 m/s multiplied by 10 s, or 200 m. The sound travels the initial 1800 m to the hill and reflects back to meet the car, covering a total distance of 1800 m + (1800 m - 200 m) = 3400 m. Dividing this total distance by 10 s gives the speed of sound as 340 m/s.

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