Question

Rajesh rows in still water with a speed of 4.5 kmph to go to a certain place and comes back. Find his 2 speed for the whole journey, if the river is flowing with a speed of 1.5 kmph?
A) 2 kmph
B) 4 kmph
C) 6 kmph
D) 8 kmph

Answer 1

5

Q:

Rajesh rows in still water with a speed of 4.5 kmph to go to a certain place and comes back. Find his average speed for the whole journey, if the river is flowing with a speed of 1.5 kmph?

A) 2 kmphB) 4 kmphC) 6 kmphD) 8 kmph

Answer:   B) 4 kmph 

Explanation:

Let the distance in one direction = k kms

Speed in still water = 4.5 kmph

Speed of river = 1.5

Hence, speed in upstream = 4.5 - 1.5 = 3 kmph

Speed in downstream = 4.5 + 1.5 = 6 kmph

Time taken by Rajesh to row upwards = k/3 hrs

Time taken by Rajesh to row downwards = k/6 hrs

Now, required Average speed =Total  

 

Therefore, the average speed of the whole journey = 4kmph.

Answer 2

$\huge{\boxed{\red {\bf{Answer}}}}$


$<b>$
Let the distance in one direction = k kms

Speed in still water = 4.5 kmph

Speed of river = 1.5

Hence, speed in upstream = 4.5 - 1.5 = 3 kmph

Speed in downstream = 4.5 + 1.5 = 6 kmph

Time taken by Rajesh to row upwards = k/3 hrs

Time taken by Rajesh to row downwards = k/6 hrs

Now, required Average speed =Total distanceTotal speed = 2kk3 + k6 = 2k x 186k + 3k = 4 kmph 

 

Therefore, the average speed of the whole journey = 4kmph.



$\huge\underline{\green {\textbf{4kmph}}}$

$<font color = purple>$

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