What was the speed of the current?

Question

We have a motor boat with a maximum water speed(the speed relative to the water its floating on) of 18mph. We make a trip upstream from our cabin to our cousins cabin, a distance of 18 miles running the bost at top speed all the way. The trip took 1 HR 12 mins. We would expect it to take 1 HR if there was no current in the river, but the current has slowed us down. How fast was the current? Assume that the river flowed at the same speech all during the trip.

Answer 1

18 mph boat speed.

upstream takes 1 hour 12 minutes = 72 minutes to go 18 miles

18 mph = 18/60 minutes = 3/10= 0.3 miles per minute

the current slowed things down, as in still water, the trip would have taken only 1 hour = 60 minutes to go 18 miles

what is the current's speed?

distance = speed times time

18 = .3(60) = (.3-c)(72) = .3(72) - 72c

72c = 21.6 - 18= 3.6

c = 3.6/72 = 0.05 miles per minute = 60(.05)/hr = 3 mph = the current's speed

18-3 = 15 mph for 1 hour and 12 minutes (1 hr 12 min = 1 hr & 12/60 hours = 1 & 1/5 hrs = 1.2 hours)

= (15mph)(1.2 hours) = 18 miles

current's speed = 3 mph or 1/20 mile per minute or 88 yards per minute or 265 feet per minute or

4.4 feet per second

3 mph is the answer you want.