Question

Velocity of boat in still water is 13m/s. If water flowes in a river with a velocity of 5 m/s, what is the difference in times taken by him to cross the river in the shortest path and in the shortest time. If the width of the river is 156m.

• A. $1sec$
• B. $\frac{13}{12}sec$
• C. $\frac{\sqrt{3}}{2}sec$
• D. $\sqrt{3}sec$

Answer 1

The correct option is A $1sec$

Shortest path taken by boat when he flow perpendicular to river with respect to river flow as shown in the fig

$t_1=\frac{156}{12}=13sec$

shortest time when he move perpendicular

$t_2=\frac{156}{13}=12sec$

$\Rightarrow diffenrence=t_1-t_2=13-12=1sec$

Hence the A option is correct.