Physics - Kinematics Question with Solution | TestHub

Let$v_r$= velocity of river

$v_{\mathrm{br}}$= velocity of river in still water and

$w$= width of river

Given,$t_{\min }= 10 \min$

or$\frac{w}{v_{\text{br}}}=10$...(i)

Drift, in this case, will be,

$x=v_{\mathrm{r}}t$

$\therefore$$120=10v_{\mathrm{r}}$...(ii)





The shortest path is taken when v_bis along$\mathrm{AB}$. In this case,

$v_{\text{b}}=\sqrt{v_{\text{br}}^2-v_r^2}$

Now,$12\text{.}5=\frac{w}{v_{\text{b}}}=\frac{w}{\sqrt{v_{\text{br}}^2-v_{\text{r}}^2}}$...(iii)

Solving these three equations, we get

$v_{\mathrm{br}} = 20 \mathrm{m} {\min }^{-1}$,

$v_{\mathrm{r}} = 12 \mathrm{m} {\min }^{-1}$

and$w= 200 \mathrm{m}$