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Model Paper 9 — Science STD 9 — Question

Gujarat BoardEnglish MediumSTD 9ScienceModel Paper 93 Marks
Question
$I.$ How will you determine the depth of a sea using echo ranging in $\text{SONAR}$ method?
$II$. A $\text{SONAR}$ device on a submarine sends out a signal and receives an echo $5s$ later. Calculate the speed of sound in water if the distance of the object from the submarine in $2625 m.$
✓

Answer

$i.$ The full name of $\text{SONAR}$ is Sound Navigation and Ranging. Sonar is based on the principle of reflection of sound wave. Powerful pulses of ultrasound are sent out at regular intervals from a transmitter mounted on a ship. When these pulses are intercepted by submerged objects, they get reflected. The reflected sound or echo is detected by an underwater receiver, which is also mounted on the ship. If speed of ultrasound be $v$ and $t$ is the elapsed time between the transmission and the reception of the ultrasound signal, the depth of the submerged object underwater is $h=\frac{V \times t}{2}$
$ii. t =5 s, h =2625 m, V =?$
$h=\frac{V \times t}{2}$
$2625=\frac{V \times 5}{2}$
$V =\frac{2625 \times 2}{5}$
$V=1050\ m / s$

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