Question

Velocity of a swimmer in still water is 5 m/s. If he
takes 10 sec to swim upstream a distance of 30 m.
then the speed of river is :-
(1) 3 m/s (2) 5 m/s (3) 10 m/s (4) 2 m/s​

Answer 1

Answer:2m/s

Explanation:Vmr=5m/s ,Tup=10sec,D=30m

so,

Vs=distance/time

      =  30/10

      = 3m/s

Vs= Vmr-Vr

=> Vr= Vmr- Vs

        = (5-3)m/s

        = 2m/s

Answer 2

The speed of the river is (d) 2 m/s.

Given: The velocity of a swimmer in still water is 5 m/s.

He takes 10 sec to swim upstream at a distance of 30 m.

To Find: The speed of the river.

Solution:

• If the velocity of a man in still water and the velocity of the man swimming upstream is given then, the velocity of the river can be found by the relation,

                  Vmr = Vm + Vr                                                   ...(1)

Where Vmr = Velocity of man in still water, Vm = Velocity of a man swimming upstream, and Vr = Velocity of the river.

Coming to the numerical, we are given;

The velocity of man in still water (Vmr) = 5 m/s

The distance traveled upstream by the swimmer = 30 m

The time is taken by him = 10 s

The upstream velocity ( Vm ) of the swimmer = 30 / 10 m/s

                                                                 = 3 m/s

So, putting respective values in (1), we get;

                    Vmr = Vm + Vr          

              ⇒   5  =  3 + Vr

              ⇒   Vr = ( 5 - 3 ) m/s

                         = 2 m/s

Hence, the speed of the river is (d) 2 m/s.

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