The most important thing to understand in vectors is that everything.. displacement, velocity, acceleration, force.. all along x axis is unaffected by what is happening along y axis and vice versa.
now, Q1. Swimming in normal dirn, man's vel is 4kmph, so he takes 1/4 hr.
and the river current gives the man a vel of 3kmph in a perpendicular dirn, so it takes him (1/4)3 km along the flow.
Q2. To reach from pt A to pt B, the resultant vel should be in direction of vector AB.. (from A to B) isnt it?? so the resultant of the vel of river + man (vector additon) should be in the normal dirn, as here vector AB is in normal dirn.
Just use vector to get the answer.. tell me if u don get it.
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