JEE Main · 2021 · 16 Mar 2021 · Shift 2 · Kinematics

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A swimmer can swim with velocity of in still water. Water flowing in a river has velocity 6 . The direction with respect to the direction of flow of river water he should swim in order to reach the point on the other bank just opposite to his starting point is ____ . (Round off to the Nearest Integer)
(Find the angle in degrees)

Answer: 120

Solution

To land at the point directly opposite, the swimmer's velocity relative to the ground must point straight across the river, so the upstream component of his swimming velocity has to cancel the current:

where is measured from the straight-across direction, on the upstream side. The direction of flow is itself from the straight-across direction, and the heading is tilted a further away from the flow, so the angle between the heading and the current is

He must swim at to the direction in which the river flows.

JEE Main · 2021 · 16 Mar 2021 · Shift 2 · Integer answer

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