The speed of a swimmer in still water is 20 m//s. The speed of river water of river water is 10 m//s and due east. If he is standing on the south bank and wishes to cross the river along the shortest path the angle at which he should make his stroke w.r.t. noth is given by :-

Options

A. `45^@` west
B. `30^@` west
C. `0^@`
D. `60^@` west

Answer

B

Explanation

For shortest path, velocity along river flow is zero
`20 sin theta = 10 rArr sin theta = 10/20 = 1/2 rArr theta = sin^(-1) (1//2)`
`theta = 30^@ west`