Question

A battalion of soldiers is ordered to swim across a river 500 ft wide. at what minimum rate should they swim perpendicular to river flow in order to avoid being washed away by the waterfall 300 ft downstream. the speed current going 3 m.p.h.

Answer 1

The time taken by the swimmer to reach the rate of 3 m/s = distance/speed

so 300/3 = 100s

And the speed at which the swimmer must swim to cross = distance/time

so 500/100 = 5m/s

Answer 2

Given that,

Width of river = 500 ft

Distance in horizontally= 300 ft

Speed of soldiers which covers 300 ft distance = 3 m/s

We need to calculate the time

Using formula of velocity

$v = \dfrac{d}{t}$

$t=\dfrac{d}{v}$

Where, v = velocity

d = distance

t = time

Put the value into the formula

$t=\dfrac{300}{3}$

$t=100\ sec$

We need to calculate the speed of soldiers to swim across a river

Using formula of velocity

$v=\dfrac{d}{t}$

Put the value into the formula

$v=\dfrac{500}{100}$

$v=5\ m/s$

Hence, The speed of soldiers to swim across a river is 5 m/s.