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Study Stuff for MCA Examinations - NIMCET
Study Stuff for MCA Examinations - NIMCET
Previous Year Question (PYQs)
A motorboat going downstream passes a raft at point A. Exactly one hour later it turned back and while coming upstream it passed the same raft at point B, 6 km from point A. What is the speed of the water current in km/hr?
Solution
Let:
Boat speed in still water = v
Current speed = c
Downstream speed = v + c
Upstream speed = v – c
Key observation:
In 1 hour, the raft (moving with the current) travels c × 1 = c km from A.
Distance between A and B = 6 km
So during the entire boat cycle, the raft moved 6 km purely due to current.
Time taken by boat after passing raft until it meets again:
Downstream for 1 hour + Upstream time (t)
Raft moves 6 km in this total time:
c × (1 + t) = 6 … (i)
Distance boat travels upstream:
(v + c) × 1 = (v – c) × t + 6
But using standard result of this classic problem:
Current speed = distance / 2
= 6 / 2
= 3 km/hr
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