A river is flowing from west to east at a speed of `5m//s`. A man on the south bank of the river capable of swimming at `10m//s` in a still water wants to swim, across the river in a shortest time. He should swim in a direction

Answer

(a) Due norht (i.e., `bot` to flow) (b) `30^(@)` west of north or at an angle `30^(@) + 90^(@) =120^(@)` from the direction of flow.

Explanation

(a) For shortest time to cross the river.
Man swin `bot^(ar)` to flow (i.e., in north ).
(b) Drift `= ( vs cos theta + v_(r) )t`
`0= (vs cos theta + v_(r) )t`
`-(v_(r))/(v_(s)) = cos theta `
`-(1)/(2) = cos theta`
` theta = 120^(@)`