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.
AL phy problem
2007-05-23 10:09 pm
回答 (1)
2007-05-23 10:50 pm
✔ 最佳答案
Resolve the velocity of swimming into two components:Velocity across the river = 4sin30o = 2 m/s
Velocity going upstream = 4cos30o = 3.46 m/s
==========
(a)
Time to take to cross the river
= displacement / velocity
= 100 / 2
= 50 s
==========
(b)
Distance upstream
= (velocity going upstream) x time
= 3.46 x 50
= 173 m
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