Q. A boat moves with a speed of $5\ km/h$ relative to water in a river flowing with a speed of $\ 3\ km/h$ and having a width of $1\ km$. The minimum time taken around a round trip is
A) 5 min
B) 60 min
C) 20 min
D) 30 min
Explanation
(d) For the round trip he should cross perpendicular to the river
$\therefore$ Time for trip to that side $= \frac{1km}{4km/hr} = 0.25hr$
To come back, again he take $0.25\ hr$ to cross the river. Total time is 30 min, he goes to the other bank and come back at the same point
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.