A person can row a boat 4m/s in still water .i) Suppose he is crossing a lake where the current is 2m/s ,in what direction will his boat be headed if he wants to reach a point directly opposite to his starting point. ii) If the lake is 200m wide how long will it take him to cross the river?
Answers
Answered by
11
Suppose the person wants cross the river flowing from North to South. He/she wants to cross from West to East.
The direction that he/she should head = Ф deg. North of East, where
Sin Ф = 2 m/s / 4 m/s = 1/2
so Ф = 30°
Then the resultant velocity will be along the direct line.
speed of the boat along direct line : 4 m/s * cos30° = 2√3 m/s
Time taken to cross the river: 200 m / 2√3 = 100/√3 seconds
The direction that he/she should head = Ф deg. North of East, where
Sin Ф = 2 m/s / 4 m/s = 1/2
so Ф = 30°
Then the resultant velocity will be along the direct line.
speed of the boat along direct line : 4 m/s * cos30° = 2√3 m/s
Time taken to cross the river: 200 m / 2√3 = 100/√3 seconds
Similar questions