A sonar signal takes 6 seconds to travel down to an underwater reef and reflect back to the vessel. If the speed of sound in water is 1500 m/s, find the depth of the reef in kilometers. MCQ with Answer and Explanation
A sonar signal takes 6 seconds to travel down to an underwater reef and reflect back to the vessel. If the speed of sound in water is 1500 m/s, find the depth of the reef in kilometers.
A. 4.8 km
B. 4.5 km
C. 4.2 km
D. 5.0 km
Answer: Option B
Solution (By JKSSB Mock Tests)
Total travel time to reef and back = 6 seconds. Time to reach reef = 3 seconds. Depth = Speed * Time = 1500 * 3 = 4500 meters = 4.5 km.
A motorboat covers a certain distance downstream in a river in 3 hours and returns upstream in 4 hours. If the speed of the river current is 3 km/h, find the speed of the motorboat in still water.
Explanation:
Let speed of boat in still water be v. Downstream speed = v + 3, Upstream speed = v - 3. Distance is same, so 3(v + 3) = 4(v - 3) => 3v + 9 = 4v - 12 => v = 21 km/h.
A thief is spotted by a policeman from a distance of 150 meters. The thief runs at 11 km/h and the policeman chases him at 12 km/h. Find the distance covered by the thief before he is caught.
Explanation:
Relative speed = 12 - 11 = 1 km/h. Time to catch the thief = 0.15 km / 1 km/h = 0.15 hours. Distance covered by thief = Speed * Time = 11 km/h * 0.15 hours = 1.65 km = 1650 meters.
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