Question

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 1

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

Answer 2

The speed of the car is 72 km/h.
=72×5/18
=20 m/s=

The distance travelled by car in 10 Seconds. 
=10×20
=200 m

Hence, the distance travelled by sound in reaching the hill and coming back to the moving driver 
=1800+(1800−200)
=3400 m

So, the speed of sound
=3400/10
=340 m/s

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