⚛️ Physics · Motion in a Plane · NEET & JEE

A river is 400 m wide flowing at 3 m/s. A swimmer swims at 5 m/s relative to water and wishes to cross straight across (shortest path). The time to cross is:

Answer: 100 s.

A 100 s
B 80 s
C 133 s
D 200 s

Correct answer: A. 100 s

Explanation: Heading upstream, resultant across = √(5² − 3²) = 4 m/s; time = 400/4 = 100 s.

Projectile trajectories launched at 15, 30, 45, 60, 75 and 90 degrees at the same speed, each annotated with range R, maximum height H and time of flight T, with coloured dots marking equal time intervals

Projectiles at equal speed: range is maximum at 45°, and complementary angles (30° and 60°) share the same range. Image: Cmglee, CC BY-SA 3.0, via Wikimedia Commons.

Concept context

Vectors, projectile motion, uniform circular motion, and relative velocity - the foundation of 2D kinematics for NEET and JEE.

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A river is 400 m wide flowing at 3 m/s. A swimmer swims at 5 m/s relative to water and wishes to cross straight across (shortest path). The time to cross is:

Concept context

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