Question

A boy claps his hand once every second and hears the echo from a distant building.He hears the echo of each clap midway between it and the next clap.If v=340m/s,what is the distance of building from the boy?

Answer 1

Given,

A boy claps his hand once every second.

He hears the echo of each clap midway between it and the next clap.

v=340m/s

To Find,

The distance of building from the boy.

Solution,

Let d be the distance of cliff from the boy .

Therefore total distance covered by sound to go to cliff and come back to boy after reflection from cliff =2d

t=0.5s (He hears the echo of each clap midway between it and the next clap)

we have , distance=speed×time ,

              2d=v×t

                  =340×0.5 ,

                d=340×0.5/2

                  =85m

Hence, the distance of building from the boy is 85m.

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Answer 2

Answer:

The distance of building from the boy is 85m.

Explanation:

Echo is the repeated sound caused by the reflection of sound waves from a surface.

Given the boy claps his hand once every second and hears the echo

He hears the echo of each clap midway between it and the next clap.

So, half the time between two seconds, therefore the time of echo is $t = 0.5sec$

Speed of sound in air, $v = 340m/s$

Let the distance between the boy and the building is d

Speed is defined as the distance travelled per unit time,

thus the distance is given by the product of speed and time.

For an echo the distance is 2d, therefore

$2d=v\times t = 340\times0.5=170 m$

$\implies d=\dfrac{170}{2} =85m$

Therefore, the distance of building from the boy is 85m.  

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