7(i)
(a) Name the waves used in SONAR.
(b) In the below diagram Lata stands between two cliffs and claps her hands. Determine the time taken by her to hear the first echo. Speed of sound in air = 320 ms-1.
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(a) Ultrasonic Waves.
(b) The closest cliff produces the first echo. However, the first cliff, or cliff A, is only 10 meters away from the Lata, and a minimum of 17 meters is required between the cliff and the listener in order to hear an echo.
Then, echo will be heard from Cliff B
Given,
Speed of sound in air (v) = 320 ms-1
Distance of Lata from cliff B (d) = 160 m
Total distance travelled = 2d = 2 × 160 = 320 m
Time = $\frac{2\text d}{\text v}=\frac {320}{320}$ = 1 sec.
Hence, the first echo will be heard after 1 second.