Question

A river of width $100m$ is flowing with a velocity of $1.5m/s$. A man start from one end with rest relative the river. He rows with an acceleration of $2m/s^2$ relative to the river. If the man want to cross the river in minimum time, by how much distance will he be drifted (flown) in the direction of river flow during the crossing.

• A. $15m$
• B. $20m$
• C. $25m$
• D. $30m$

Answer 1

The correct option is A $15m$

From $\text{A}$ to $\text{B}$ in y-direction,

${\text{S}}_{\text{y}}={\text{u}}_{\text{y}}t+\frac{1}{2}{\text{a}}_{\text{y}}{\text{y}}^2$

$100=0+\frac{1}{2}\left(2\right)t^2$

$t=10sec$.

From $\text{A}$ to $\text{B}$, in x-direction,

${\text{S}}_{\text{x}}={\text{u}}_{\text{x}}t$

${\text{S}}_{\text{x}}=\left(1.5\right)\times \left(10\right)=15m$.