A boat can travel at speed of 12km/h in still water.If it takes 3 hrs to go 15km upstream and back. Find the speed of current.
2007-03-17 15:59:15 · 1 answers · asked by netwiyan 1 in Science & Mathematics ➔ Mathematics
the total time of the trip is known, 3 hours. the total time is the sum of the time to go up plus the time to go down stream.
The time is the distance (15) divided by the net speed. Going up the current works against the boat so the net speed is 12-v, coming back the current helps the boat so the net speed is 12 + v.
The overall equation then is
3 = up plus down = 15/ [12 - v] plus 15/[12+v]
3 = [15 [12+v] + 15 [12 - v] ]/[[12-v][12+v]]
3= [180 + 15v + 180 - 15v ]/[144-v**2]
432 - 3v**2 = 360
v= root 24 = 4.899 km/hr
using this value, the upstream time was 2.11 hour and coming back was 0.89 hour.
2007-03-17 16:46:03 · answer #1 · answered by lare 7 · 0⤊ 0⤋