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Question: Answered & Verified by Expert
A boat moves with a speed of $5 \mathrm{~km} / \mathrm{h}$ relative to water in a river flowing with a speed of $3 \mathrm{~km} / \mathrm{h}$ and having a width of 1 $\mathrm{km}$. The minimum time taken around a round trip is
PhysicsMotion In Two DimensionsJEE Main
Options:
  • A 5 min
  • B 60 min
  • C 20 min
  • D 30 min
Solution:
2510 Upvotes Verified Answer
The correct answer is: 30 min
For the round trip he should cross perpendicular to the river $\therefore$ Time for trip to that side $=\frac{1 \mathrm{~km}}{4 \mathrm{~km} / \mathrm{hr}}=0.25 \mathrm{hr}$ To come back, again he take $0.25 \mathrm{hr}$ to cross the river.
Total time is $30 \mathrm{~min}$, he goes to the other bank and come back at the same point.

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