Swimmer's problem or River-boat problem:
I.cl $V_{1 v}=$ velocity of water w.r.t ground Vs, $w=$ velocity of swimmer w.r.t. water $V_{s}=$ velocity of swimmer w.r.l. ground
Now, $A C=V_{s}^{\prime} \times$ crossing time $t$
$\Rightarrow \quad(A B+B C)=\left(V_{s, w}^{\prime}+V_{w}^{\prime}\right)$
$\Rightarrow \quad(d \hat{j}+x \hat{i})=\left[\left(-V_{s, w}^{\prime} \sin \theta\right) \hat{i}+\left(V_{s, 18} \cos \theta\right) \hat{j}+i_{w} \hat{i}\right] t$
$\left.\Rightarrow \quad(x \hat{i}+d \hat{j})=\left(V_{v}-V_{s, 1 \mathrm{~F}} \sin \theta\right) t \hat{i}+\left(\ddot_{t, v} \cos \theta\right) t \hat{j}\right)$
i.c. $\quad x=\left(V_{w}-V_{A, v} \sin \theta\right) t$
and $d=\left(V_{s, v} \cos \theta\right) t \quad \Rightarrow \quad i-\frac{d}{\left(\sigma_{n, w}{\cos \theta)}\right.} \quad \ldots(3)$