1.

A car moving with a speed of 72kmph towards a hill. car blows horn at a distance of 1800m from the hill. if echo is heard after 10s, the speed of sound (ms-1) is

Answer»

Speed of car = 72 km /h= 72×10^3/36×10^2=
20 m/s .
SOUND is heard after 10s and after ten second of blowing the HORN the car will be at a POSITION 'B' '200 m' away from the starting point 'A' .
The TOTAL distance travelled by the sound therefore = 1800 m + (1800 - 200) m =
3400 m .
So, now we know the distance travelled and the TIME taken by the sound to complete an echo .
By using the formula ,
SPEED = DISTANCE / TIME, we get,
3400/10 = 340 m/s

Hence the speed of sound is 340 ms^-1


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