Question

A man can swim in still water with a velocity $5m/s$. He wants to reach at directly opposite point on the other bank of a river which is flowing at a rate of $4m/s$. River is $15m$ wide and the man can run with twice the velocity as compared with velocity of swimmer with respect to river. If he swims perpendicular to river flow and then run along the bank. Time, in seconds, taken by him to reach the opposite point is

• A. 4
• B. 4.2
• C. 5.4
• D. 3.6

Answer 1

The correct option is B 4.2

from A to B then P
$V_{m/r}.t_2=AB$

$V_m.t_2=d$
$V_{m/r}$ is swimming velocity of man w.r.t river

$V_m$ is swimming velocity man
Given $V_m=5m/s$
$t_2=\frac{d}{V_m}=\frac{15}{5}=3sec$
and $t_3$ from B to P
$t_3=\frac{D}{V_{mW}}=\frac{4\times 3}{5\times 2}=1.2s$
$V_{mW}=$walking speed of man
total time $t=t_2+t_3=4.2sec.$