Question

The distance between two piers on a river is 43.2 miles. It takes a motorboat, moving downriver, 2 hr 24 min to complete the journey. How much time does it take the same boat to go back upstream if the current flows at 1.8 mph

Answer 1

Answer:

Time taken by same boat to go back upstream is 3 hours .

Explanation:

Given :

Current flow , u = 1.8 mph .

Distance between two piers on a river , d = 43.2 miles .

Time taken to move downstream is 2 hr 24 min  i.e $2+\dfrac{24}{60}=2.4\ hr\ .$

Let , speed of boat be v .

Therefore ,

$v+u=\dfrac{43.2}{2.4}\\\\v+1.8=18\\\\v=16.2\ m/s\ .$

Now , time taken to go same distance in upstream .

$t=\dfrac{43.2}{v-u}\\\\t=\dfrac{43.2}{16.2-1.8}\\\\t=3\ hours$

Therefore , time taken by same boat to go back upstream is 3 hours .

Hence , this is the required solution .

Answer 2

The time taken does it take the same boat to go back upstream if the current flows at 1.8 mph is 3 hours.

Calculation of the time taken:

Since

Current flow , u = 1.8 mph .

Distance between two piers on a river , d = 43.2 miles.

Now for down stream should be

= 2 hr 24 min

= 2 + 24/60

= 2.4 hour

Let us speed of the boat be x

So,

u + v = 43.2 / 2.4

v + 1.8 = 18

v = 16.2 m/s

Now the time taken should be

= 43.2 / v - u

= 43.2 / 16.2-1.8

= 3 hours

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