Question

A swimmer swims with a speed 5 m/s w.r.t.river.
The minimum time, the swimmer would take, to
cross the river of width 300 m will be
(1) 60 s
(2) 30 s
(3) 10 s
(4) 5 S​

Answer 1

remember that speed=distance/time

therefore,

time=distance/speed

=60s

Answer 2

The swimmer requires (1)60 seconds to cross the river.

Given,

Speed of the swimmer with respect to river=5 m/s

Width of the river=300 m.

To find,

the minimum required by the swimmer to cross the river.

Solution:

• The concept here is from the chapter "Motion in a plan".
• As the relative velocity of the swimmer with respect to the river is already given as 5 m/s, we don't have to find the relative motion between the river and the swimmer.
• We will simple concept of speed here.
• Speed of an object is equal to the ratio of the distance covered and the time taken to cover that distance.
• $Speed=\frac{Distance}{Time} \\Time=\frac{Distance}{Speed}$.

The time required by the swimmer to cross the river will be:

$Time=\frac{300}{5}\\ Time=60 seconds.$

Hence, 60 seconds are required by the swimmer to cross the river.

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