Question

A boat sails 18 km of a river stretch upstream in 6 hours and takes only 4.5 hours to cover the same distance downstream.what is the speed of the current?
1.5 kmph
1 kmph
0.5 kmph
2 kmph​

Answer 1

Answer:

bro speed of current or speed of boat...

If speed of boat then 2kmph at upstream and 4kmph at downstream...

for river stream the 4kmph-2kmph then speed of stream is 2kmph

Hence option D

Answer 2

Answer:

The speed of the current is $0.5kmph.$

Step-by-step explanation:

In downstram, direction of current flow is same as of boat while in upstream current flows against the boat.

So, the relative speed in downstean

           $(S_d)=$ Speed of boat $(S_b)$ $+$ Speed of current flow $(S_c)$

and, the relative speed inupstream

           $(S_u)=$ Speed of boat $(S_b)$ $-$ Speed of current flow $(S_c)$

        $Speed=\frac{Distance}{Time}$

In upstream

Given,

Distance $=18km$

     Time $=6hrs$

Relative speed, $S_u$ $=\frac{18}{6} =3kmph$

                          $S_u=S_b-S_c$

⇒  $S_b-S_c=3...eq(i)$

In downstream

Given,

Distance $=18km$

     Time $=4.5hrs$

Relative speed, $S_d$ $=\frac{18}{4.5} =\frac{180}{45} =4kmph$

                          $S_d=S_b+S_c$

⇒  $S_b+S_c=4...eq(ii)$

On adding $eq(i)$ and $eq(ii)$ we get

$2$ × $S_b=7$

⇒ $S_b=3.5kmph$

On putting $S_b=3.5kmph$ in $eq(i)$ we get,

$S_b-S_c=3...eq(i)$

$3.5-S_c=3$

        $S_c=0.5kmph$