A motorboat covers 12 km upstream and returns back to the starting jetty in 3 hours. If the speed of the boat in still water is 9 km/h, find the speed of the river current. MCQ with Answer and Explanation
A motorboat covers 12 km upstream and returns back to the starting jetty in 3 hours. If the speed of the boat in still water is 9 km/h, find the speed of the river current.
A. 3 km/h
B. 5 km/h
C. 4 km/h
D. 2 km/h
Answer: Option A
Solution (By JKSSB Mock Tests)
Let the speed of the current be c km/h. 12 / (9 - c) + 12 / (9 + c) = 3. Dividing by 3: 4 / (9 - c) + 4 / (9 + c) = 1 => 4(9 + c + 9 - c) = 81 - c^2 => 72 = 81 - c^2 => c^2 = 9 => c = 3 km/h.
A motorboat rows 30 km downstream in 3 hours and tracks the identical route upstream back to the jetty point in 6 hours. Find the net speed index of the current stream flow.
A person can row 8 km/h in still water. If the river current flows at 4 km/h, it takes him 4 hours to row to an outpost and back. Find the distance of the outpost.
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