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Question

A swimmer's speed in the direction of the flow of river is 16 km/h. Against the direction of flow of river, the swimmer's speed is 8 km/h. Calculate the swimmer's speed in still water and speed of flow of the river respectively..

A
12 km/h, 4 km/h
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B
10 km/h, 3 km/h
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C
10 km/h, 4 km/h
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D
12 km/h, 2 km/h
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Solution

The correct option is A 12 km/h, 4 km/h
Let the direction of flow of river as +ve.
swimmer's speed in still water means speed of swimmer w.r.t river flow,
vs,r=vsvr ...(i)
given that
where vs= speed of swimmer w.r.t ground
vr= speed of river flow w.r.t ground
When swimming in direction of river flow
vs=+16 km/h
vs,r=16vr ...(ii)
When swimming in direction opposite of river flow
( direction of swimmer will be ve)
vs=8 km/h
vs,r=8(+vr) ...(iii)
Adding Eq (ii) & (iii),
2vr=8
vr=4 km/h
Hence, from Eq (i),
vs,r=164=12 km/h
option (a) is correct.

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