Question

A boat-man can row a boat to make it move with
a speed of 10 km/h in still water. River flows steadily
at the rate of 5 km/h. and the width of the river
is 2 km. If the boat man cross the river along the
minimum distance of approach then time elapsed
in rowing the boat will be :​

Answer 1

Hey Dear,

◆ Answer -

t = 0.2309 h = 13 min 51 s

● Explanation -

# Given -

vb = 10 km/h

vr = 5 km/h

# Solution -

Minimum distance of approach will be equal to width of river.

s = 2 km

For the man to travel perpendicular to river stream, effective speed will be -

v = √(vb^2 - vr^2)

v = √(10^2 - 5^2)

v = √(100 - 25)

v = √75

v = 5√3 km/h

Now, time taken by man in boat to cross river is -

t = s / v

t = 2 / 5√3

t = 0.2309 h

t = 13 min 51 s

Therefore, time taken by man to cross is 13 min 51 s.

Hope this helps you...