Question

A boat moves perpendicular to the bank of a stream with a velocity of $7.2\text{km/h}$. The current carries it $150\text{m}$ downstream, the time required to cross the river is
(The width of the river is $0.5\text{km}$)

• A. $4.16\text{min}$
• B. $2.15\text{min}$
• C. $3.11\text{min}$
• D. $5.11\text{min}$

Answer 1

The correct option is A $4.16\text{min}$

As the boat moves perpendicular to stream of water ,it is the case of shortest time.
So,
$t=\frac{w}{v}$
$t=\frac{0.5\text{km}}{7.2\text{kmph}}=\frac{0.5}{7.2}\times 60\text{min}t=\frac{5}{12}\times 10=4.16\text{min}$