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 time taken around a round trip is
J & K CETJ & K CET 2005Motion in a Plane
Solution:
Time taken by the boat to reach the other side is
Time $=\frac{\text { distance }}{\text { relative speed }}$
Relative speed $10\, m m=\sqrt{5^{2}-3^{2}}-\sqrt{16}=4\, k m\, h^{-1}$
$T=\frac{1 \,km }{4\, kmh ^{-1}}=0.25\, h$
To come back boat takes the same time, hence total time is
$T' =2 \times 0.25=0.5 \,h$
Also, $1 \,h =60 \,min$
$\therefore 30\, mm \,0.5\, h =30 \,min$
