A RADAR sends a signal to an aeroplane at a distance 45 km away with a speed of 3 × 10 8 m s - 1 . After how much time is the signal received back from the aeroplane?

We know that, S p e e d o f s o u n d V = T o t a l d i s tan c e t r a v e l l e d 2 d t i m e i n t e r v e l t Total distance travelled by the sound in going and then coming back = 2 d Given, d = 45 km Converting km to m , we get, Therefore, 45 km = 45 , 000 m Hence, d = 45 × 10 3 m V = 3 × 10 8 m s - 1 Substituting the values in the formula above, we get, V = 2 d t 3 × 10 8 = 2 × 45 × 10 3 t t = 90 × 10 3 3 × 10 8 = 3 10 4 t = 3 × 10 - 4 Hence, the signal is received back after 3 × 10 - 4 s .

E M B I B E

Selina Icse Concise Physics For Class 10>Chapter 7 - Sound>EXERCISE-7(A)>Q 3

HARD

10th ICSE

IMPORTANT

Earn 100

What should be the minimum distance between source and reflector in water, so that echo is heard distinctly?
(The speed of sound in water $= 1400 m s^{- 1}$ )

Important Questions on Sound

HARD

10th ICSE

IMPORTANT

Selina Icse Concise Physics For Class 10>Chapter 7 - Sound>EXERCISE-7(A)>Q 4

A man standing

25 m

away from a wall produces a sound and receives the reflected sound. Calculate the time after which he receives the reflected sound if the speed of the sound in air is

350 m s^{- 1}

.

HARD

10th ICSE

IMPORTANT

Selina Icse Concise Physics For Class 10>Chapter 7 - Sound>EXERCISE-7(A)>Q 4

A man standing

25 m

away from a wall produces a sound and receives the reflected sound. If the speed of the sound in the air is

350 m s^{- 1}

will the man be able to hear a distinct echo? Explain the answer.

HARD

10th ICSE

IMPORTANT

Selina Icse Concise Physics For Class 10>Chapter 7 - Sound>EXERCISE-7(A)>Q 5

A RADAR sends a signal to an aeroplane at a distance

45 km

away with a speed of

3 \times 10^{8} m s^{- 1}

. After how much time is the signal received back from the aeroplane?

HARD

10th ICSE

IMPORTANT

Selina Icse Concise Physics For Class 10>Chapter 7 - Sound>EXERCISE-7(A)>Q 6

A man standing

48 m

away from a wall fires a gun to calculate the time after which an echo is heard. (The speed of sound in air is

320 m s^{- 1}

).

HARD

10th ICSE

IMPORTANT

Selina Icse Concise Physics For Class 10>Chapter 7 - Sound>EXERCISE-7(A)>Q 7

A ship on the surface of water sends a signal and receives it back from a submarine inside water after

4 s

. Calculate the distance of the submarine from the ship. (The speed of sound in water is

1450 m s^{- 1}

)

HARD

10th ICSE

IMPORTANT

Selina Icse Concise Physics For Class 10>Chapter 7 - Sound>EXERCISE-7(A)>Q 8

A pendulum has a frequency of

5

vibrations per second. An observer starts the pendulum and fires a gun simultaneously. He hears an echo from the cliff after

8

vibrations of the pendulum. If the velocity of sound in air is

340 m s^{- 1}

, find the distance between the cliff and the observer.

HARD

10th ICSE

IMPORTANT

Selina Icse Concise Physics For Class 10>Chapter 7 - Sound>EXERCISE-7(A)>Q 9

A person standing between the two vertical cliffs produces a sound. Two successive echoes are heard at $4 s$ and $6 s$ . Calculate the distance between the cliffs. (speed of sound in air $= 320 m s^{- 1}$ )