Question

2. Crack of thunder is heard after 10 seconds of
lightning. How high is the cloud from an observer?
Take speed of sound 332 ms-1​

Answer 1

Given:

Crack of thunder is heard after 10 seconds of lightning. Speed of sound in air is 332 m/s.

To find:

Height of cloud from observer ?

Calculation:

First of all, let's understand the physics of these question :

• When a lightning-thunder occurs in the cloud, the light (electromagnetic waves) travel much faster due to higher speed than sound waves.

• Now, sound waves travelling at a much slower speed reach the observer after sometime as compared to the light.

• Thats why we say that lightning is seen first and then the thunder is heard.

So, the question says that the thunder was heard after 10 seconds by an observer presumably standing on earth surface.

So, let the height traversed by the sound wave be H :

$\sf \therefore \: H = speed \times time$

$\sf \implies\: H =332 \times 10$

$\sf \implies\: H =3320 \: metres$

$\sf \implies\: H =3.32\: km$

So, the cloud is situated 3.32 km above the observer.

Answer 2

Answer:

The speed of sound- 332 m/s

Time taken - 10 sec

Distance= speed×time

= 332 ×10

=3320m

Distance in km= 3320/1000=3.32km