AL phy problem

Question

A man swims across a river 100m wide always leaning upstream at an angle of 30 with the bank
(a)How long does he take to cross the river if he swims at 4m/s and the water flows at 16km/h?
(b)Find how far upstream from the point at which he would be reached if the water is still,assuming that he keeps swimming straight for all time.

Answer 1

Resolve the velocity of swimming into two components:
Velocity across the river = 4sin30o = 2 m/s
Velocity going upstream = 4cos30o = 3.46 m/s

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(a)
Time to take to cross the river
= displacement / velocity
= 100 / 2
= 50 s

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(b)
Distance upstream
= (velocity going upstream) x time
= 3.46 x 50
= 173 m