If Johnny can row at 5 kmph in still water. If the velocity of the current is 1 kmph and it takes him 1 hour to row to the supply ship and come back, how far is the supply ship ?
Answers
Assume the distance between Johnny and the supply ship be X Km .
Given that Velocity of Johnny in still water = 5 kmph.
Velocity of the current = 1 kmph.
If we consider that velocity of current is in favor of the direction of the boat of Johnny , then effective speed of Johnny shall be sum of the velocity of Johnny and current ie
.∴ Velocity by which Johnny wil go = 5 + 1= 6 kmph.
∴ Time taken by Johnny to reach the ship is (t1) = X/6
since velocity =distance/time.
While return journey Johnny will be rowing against the current.
So, net velocity will be .Net Velocity = 5 - 1= 4 kmph.
So, time taken in return journey : t2 =X/4.
According to the problem time taken BY Johnny for going and coming back=1hr .
Therefore, t1 +t2=1 hr.
Or, X/6+X/4=1. or, (2X+3X)/12=1.
or, 5X/12 =1
Therefore, distance X is 12/5=2.4 km
∴Distance between the Johnny and the Supply ship is 2.4 km. Answer