Question

A boy clapped near a rock and after 3 seconds he heard an echo. If the speed of the sound is 346 ms^-1, then how far is the boy from the rock?
1. 219 meter
2. 341 meter
3. 346 meter
4. 519 meter

Answer 1

Correct Answer - Option 4 : 519 meter

The correct answer is 519 meters.

Speed of Sound = 346 ms^-1     (A)

Time is taken to echo the be heard = 3 second

• Let’s consider the distance between the boy and rock = d

Now, In order to echo to be heard the sound had to 1^st travel to the rock and then come back.

• This means the sound has to cover distance= 2d 

According to the question, Time is taken to travel 2d distance = 3 s

So, Time to travel distance d = 3/2 sec    (B)

Now, Distance = Speed × Time

                          = 346 ms^-1 \(×3/2\)s [From (A) and (B)]

                          = 519 m

So, the distance between the boy and the rock(d) = 519 m