Question

Q.11 A boy hear the echo of his own voice from a distance hill after 0.8second. If the speed of the sound in air is 340 m/s. Calculate the distance of hill from the boy.​

Answer 1

Speed of the sound (S) = 340 m/s

Time taken to travel (t) = 0.8 s

Distance of hill from the boy (d) = ? m

Total distance to hear echo = 2d

[ ∵ Sound reflects back after hitting the hill . Here total distance is given by distance from the boy to hill and from hill to boy , which is nothing but ' 2d ' ]

We know that , ' Speed is defined as distance traveled per unit time '

➠ $\sf \pink{Speed=\dfrac{Distance}{Time}}$

➠ $\sf S=\dfrac{2d}{t}$

➠ $\sf 340=\dfrac{2d}{0.8}$

➠ $\sf 2d=272$

➠ $\sf \green{d=136\ m}\ \; \bigstar$

Distance of hill from the boy is 136 m .

Answer 2

Answer:

Given :-

• A boy hear the echo of his own voice from a distance hill after 0.8 seconds. If the speed of the sound in air is 340 m/s.

To Find :-

• What is the distance of hill from the boy.

Formula Used :-

$\boxed{\bold{\large{Speed =\: \dfrac{Distance\: Travelled}{Total\: Time}}}}$

Solution :-

Let, the distance travelled by echo be 2d.

• Speed = 340 m/s
• Total time = 0.8 s

According to the question by using the formula we get,

⇒ $\sf 340 =\: \dfrac{2d}{0.8}$

⇒ $\sf 340 =\: \dfrac{2d \times 10}{8}$

⇒ $\sf 340 =\: \dfrac{20d}{8}$

By doing cross multiplication we get,

⇒ $\sf 20d =\: 340 \times 8$

⇒ $\sf 20d =\: 2720$

⇒ $\sf d =\: \dfrac{\cancel{2720}}{\cancel{20}}$

➠ $\sf\bold{\red{d =\: 136\: m}}$

$\therefore$ The distance of hill from the boy is 136 m .