A river is flowing from west to east at a speed 15m/s. a boy on the south bank of the river,capable of swimming at 30m/s wants to swim, cross the river in the shortest time. He should swim in direction?

a)due north   b)30* east of north  c)30* west of north  d)60* east of north.

Give me the solution of this qn nd also give the figure. Answer is a.

WHERE   *  MEANS DEGREE

to reach in shortest time the vertical component of velocity should be maximum so HE SHOULD SWIM DUE NORTH