jack cruised 42 miles downriver in 45 min (0.75 hr.)
His return trip took 1 hr. Determine the average speed of his motorboat in still water and the average speed of the river current??
2006-11-20 04:06:39 · 3 answers · asked by Erica C 1 in Science & Mathematics ➔ Geography
rate * time = distance
Let s be rate in still water
Let r be rate of current
Then s+r = rate downriver = 42/.75= 56
rate upstream = r-s =42/1 = 42
Add these two equations to get:
2r = 98
r= 49 = rate in still water
s=r-42 = 49-42= 7 = speed of current
2006-11-20 05:19:11 · answer #1 · answered by ironduke8159 7 · 0⤊ 0⤋
not entirely sure about this one because im wondering if gravity assisted in his speed down the river. I think that ignoring that the average speed is half the difference + 45mins so 15/2 = 7 1/2 mins so the average sped in still water is 52 1/2 mins
The average speed of the current i imagine would be the difference . However I'm not certain this is just in case you don't get any better answers. Good luck though - that was confusing
2006-11-20 12:18:58 · answer #2 · answered by nax 2 · 0⤊ 0⤋
r=rate
d=distance
t=time
r=d/t
r=42/.75
r=56mph downstream
r=42mph upstream
the current would be 1/2 the difference between 56 and 42 since it adds to the speed downstream and subtracts from upstream. so the current is 7mph. so the average speed in still water would be 49mph
2006-11-20 12:29:06 · answer #3 · answered by nutsnflats 2 · 0⤊ 0⤋