Physics, asked by YasinKhan, 1 year ago

Streamer moves with velocity 3 km per hour in and against the direction of river water whose velocity is 2 kilometre per hour calculate the total time for total journey if the boat travels 2 km in the direction of steam and then back to its place

Answers

Answered by 2002yashagarwal

velocity of streamer = 3kmph
velocity of river = 2kmph
relative velocity =velocity of streamer -vel of river
=3-2=1kmph
distance = 2kms
time1=d\s=2hrs
rel velocity in oppositedirection =3+2=5kmph
time2=2\5 hrs =24 minutes
total time =t1+t2 =120mins +24mins=144mins

YasinKhan: tysm

rjofspecoyqpg1: Here answer is right. But method is not correct. A boat will take less less time to go downstream because of more resultant velocity ( water supports motion). Also it takes more time to go upstream as the effective velocity is less( water opposes motion)

rjofspecoyqpg1: One must take resultant velocity and not relative velocity. When boat goes upstream effective velocity will be less, time taken will be more but relative velocity will be high.

Answered by rjofspecoyqpg1

When the steamer go along the flow it speed is 3kmph +2 kmph = 5 kmph
Time taken to travel downstream is $t_1 = \frac{distance}{effective\: speed}$ .
$\therefore t_1 = \frac{2\:km}{5\:kmph}\:=\:0.4\:h$ .

When the steamer go against the flow it speed is 3kmph -2 kmph = 1 kmph
Time taken to travel upstream is $t_2 = \frac{distance}{effective\: speed}$ .
$\therefore t_2 = \frac{2\:km}{1\:kmph}\:=\:2\:h$

Total time = 2 +0.4 = 2.4 h.

It is two hour and twenty four minutes.

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