question_answer

A river is flowing from W to E with a speed of 5 m/min. A man can swim in still water with a velocity 10 m/min. In which direction should the man swim so as to take the shortest possible path to go to the south.    [BHU 2005]

A)               30° with downstream             

B)                          60° with downstream         

C)                          120° with downstream           

D)                          South

Correct Answer: C

Solution :

              For shortest possible path man should swim with an angle (90+q) with downstream.             From the fig, \[\sin \theta =\frac{{{v}_{r}}}{{{v}_{m}}}=\frac{5}{10}=\frac{1}{2}\] Þ  \[\therefore \] q = 30°          So angle with downstream = \[90{}^\circ +30{}^\circ =120{}^\circ \]