Question

a sailor goes 15 kilometre downstream in 1 hour and returns back to the starting point in 1 hour 40 minutes find the speed of the Sailor in still water and the speed of the stream ​

Answer 1

let u be the downstream and v be the up stream

$\frac{u + v}{u - v} = \frac{100}{60} (in \: min) \\ \frac{u + v}{u - v} = \: \frac{5}{3} \\ applying \: c \: and \: rule \\ \frac{u}{v} = \frac{8}{2}$

u = 4km/ hr

v= 1km/hr

Answer 2

Answer:

Speed of the sailor in still water = 12 km/h

Speed of the stream = 3 km/h

Step-by-step explanation:

Given, that the problem is -

• There is a sailor who goes 15 km downstream. This means The displacement/distance traveled will be 15 km.
• It takes 1 hour to reach the destination downstream
• It takes 1 hour and 40 minutes to reach the starting point.

Let,

Speed of the sailor in still water= v

Speed of the stream = u

In downstream -

The relative speed will be the addition of the speed of the sailor and stream because both are in the same direction. Also, it would take 1 hour to reach the destination.

$(v+u) t = s\\\\(v+u)\times 1 = 15\\\\v+u = 15$equation (i)

In upstream -

The relative speed will be the difference between the speed of the sailor and the stream because both are in the opposite direction. Also, it would take 1 hour and 40 minutes to reach the destination.

t = 1 hour 40 min = $1\frac{2}{3} \ hours = \frac{5}{3} \ hours$

$(v-u) t = s\\\\(v-u)\times \frac{5}{3}= 15\\ \\v-u = 9$equation (ii)

Adding equation (i) and equation (ii)

$2v = 24\\\\v = 12\ km/h$

Putting the value of v in equation (i)

$v + u = 15\\\\12+u=15\\\\u = 3 \ km/h$

So,

Speed of the sailor in still water = 12 km/h

Speed of the stream = 3 km/h

#SPJ3