Question

Minimum distance between the observer and the obstacle for echo to be heard​

Answer 1

Answer:

• Minimum distance between the observer and the obstacle for the echo to be heard clearly should be 17.2 m.and the temperature should be 25°c

Answer 2

${\large{\underline{\underline{\mathfrak{Solution:-}}}}}$

Let distance between the observer and the obstacle = d

Speed of sound (in the medium) = v

Time after which echo is heard = t

$\fbox{\fbox{\large{\bold{Then,}}}}$

$t = \frac{2d}{v} \: or \: d = \frac{vt}{2}$

$\fbox{\fbox{\large{\bold{We\: know}}}}$

Speed of sound in air at 20°C

$= 343m \: \: {s}^{ - 1}$

For an echo to be heard distinctly,

$t \: \geqslant 0.1s$

$then \: \: \: d \geqslant \frac{343 m \: {s}^{ - 1} \times 0.1s }{2 \:} \: or \: \: d \geqslant 17.2m$

Thus, the minimum distance (in air at 20°C ) between the observer and the obstacle for the echo to be heard clearly should be 17.2 m.