# CBSE Class 11-science Answered

A boy swims in a straight line to reach the other side of a river .His velocity is 5m/s and the angle of swim with the shore is 30 degree . Flow of river opposes his movement at 2 m/s.If width of river is 200m,where does he reach the other bank?

Asked by Samhitha P.S | 25 Sep, 2019, 06:24: PM

Expert Answer

If the boy swims at velocity 5 m/s in a direction that makes angle 30° with shore,

then the velocity is resolved in a direction parallel to river flow as 5cos30 m/s = 5√3/2 m/s = 4.33 m/s

and another direction perpendicular to river flow as 5sin30 m/s = 2.5 m/s.

if the river width is 200 m, then time to reach the other bank = 200/2.5 = 80 s

since river flow opposes the swimmer, resultant velocity opposite to flow direction is (4.33-2 ) m/s = 2.33 m/s

Horizontal distance travelled = 2.33 × 80 = 186.4 m from starting point

Answered by Thiyagarajan K | 25 Sep, 2019, 07:13: PM