Alicia intends to swim to a point straight across a 100 m wide river with a current that flows at 1.2 m/s. She can swim 2.5 m/s in still water. At what angle, measured from the upstream direction, must she swim upstream to achieve her goal

θ = 61.3°

She must swim at an angle of 61.3°

Explanation:

Given;

Width of river = 100 m

Alicia speed in still water = 2.5m/s

Current of river = 1.2m/s

The angle for her to achieve her goal can be derived by the summation of velocity in the direction of the current.

Her speed in the opposite direction of the current must be able to neutralise the speed of the current;

2.5cosθ - 1.2 = 0

2.5cosθ = 1.2

cosθ = 1.2/2.5

θ = cosinverse(1.2/2.5)

θ = 61.3°

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