A man can swim with a speed of 4 km h-1 in still water. He crosses a river 1 km wide that flows steadily at 3 km h-1. If he makes his strokes normal to the river current, how far down the river does he go when he reaches the other bank?

Question

A man can swim with a speed of 4 km h-1 in still water. He crosses a river 1 km wide that flows steadily at 3 km h-1. If he makes his strokes normal to the river current, how far down the river does he go when he reaches the other bank? (A) 500 m (B) 600 m (C) 750 m (D) 850 m

Tardigrade Admin · Accepted Answer

Time to cross the river, t=( textWidth of river/ textSpeed of man) =(1 km/4 km h-1) =(1/4)h Distance moved along the river in time t, s=vr× t=3 km h-1×(1/4)h=(3/4)km =750 m

Q. A man can swim with a speed of $4 km h^{- 1}$ in still water. He crosses a river $1 km$ wide that flows steadily at $3 km h^{- 1}$ . If he makes his strokes normal to the river current, how far down the river does he go when he reaches the other bank?

$500 m$

$600 m$

$750 m$

$850 m$

Time to cross the river,
$t = \frac{Width of river}{Speed of man}$
$= \frac{1 km}{4 km h ^{- 1}}$
$= \frac{1}{4} h$
Distance moved along the river in time $t$ ,
$s = v_{r} \times t = 3 km h^{- 1} \times \frac{1}{4} h = \frac{3}{4} km$
$= 750 m$

Q. A man can swim with a speed of 4kmh−1 in still water. He crosses a river 1km wide that flows steadily at 3kmh−1. If he makes his strokes normal to the river current, how far down the river does he go when he reaches the other bank?

500m

600m

750m

850m