Question

what should be the minimum distance of sound source from the reflecting surface so that echo of the sound can be heard?(Assume the speed of sound in air is 344 m/s)
a) 25.0 cm
b) 17.2 m
c) 8.25 m
d) 2.5 m
e) none of these ​

Answer 1

$\underline{\sf{Answer:-}}$

• 17.2m

$\underline{\sf{\green{Solution:-}}}$

$\underline{\sf{Given:-}}$

• $\bold{V_{air} = 344m/s}$
• $\bold{t = 0.1 Sec. }$

$\pink{\bigstar} \boxed{\green{\bold{2S = Vt}}}$ WHY?

Putting values -

$\bold{2S = Vt}$

$\bold{S=\frac{Vt}{2}}$

$\bold{S=\frac{\cancel{344}^{172}×0.1}{\cancel{2}}}$

$\bold{S=172×0.1}$

$\implies\boxed{\underline{\bold{\red{\bold{S= 17.2m}}}}}$ Ans.

_______________________

WHY?

$\bold{\boxed{\bold{\green{2S = Vt}}}}$

Here -

• S = Distance of Sound
• V = Velocity
• t = Time

because

$\boxed{\bold{S + S_{Reflected \: Sound} = Velocity × time \:taken}}$

@itzMeGunjan

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