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An ultrasonic pulse sent from a ship to the sea floor returns after 1.6 s. If sound travels at 1400 m/s in seawater, what is the depth of the sea?
A560 m
B2240 m
C1120 m
D4480 m
Answer & Solution
Correct answer: C. 1120 m
1. Note the data: time $t = 1.6\,\text{s}$ and speed $v = 1400\,\text{m/s}$.
2. The pulse goes down to the floor and back, covering a total distance of $2d$.
3. So $2d = v \times t = 1400 \times 1.6 = 2240\,\text{m}$.
4. Hence $d = \dfrac{2240}{2}$.
5. Therefore the depth $d = 1120\,\text{m}$.
6. Trap C (2240) forgets the factor of 2 for the return trip; trap A (560) halves once too many.
_Source: Samacheer Kalvi (TN SCERT) Class 10 Science, Unit 5 Acoustics "Acoustics", p.78_
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