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Echoes and Vibrations of Sound — Physics STD 10 — Question

ICSE BoardEnglish MediumSTD 10PhysicsEchoes and Vibrations of Sound5 Marks
Question
A person standing between two vertical cliffs and is $640$ m away from the nearest cliff. He shouted and heard the first echo after $45s$ and the second echo after further $3s$. Calculate the speed of sound in air and the distance between the cliffs.
✓

Answer

Given: $d_1 = 640m; t_1 = 4s$
$t_2 = 4 + 3 = 7$
First echo is heard from the nearest cliff.
Total distance travelled = 2d = 2 × 640 = 1280 m
$v=\frac{2 d _1}{ t _1}=\frac{1280}{4}=320 m / s$
Second echo is heard from the first cliff
$v =\frac{2 d _2}{ t _2}$
$\Rightarrow 320 ms ^{-1}=\frac{2 d _2}{7}$
$d _2=\frac{320 \times 7}{2}=1120 m$
hence, the distance between two cliff
$d_1 + d_2 = 640 + 1120 = 1760 m.$

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