A boat moves through the water of a river at 8 m/s relative to the water, regardless of the boat's direction. If the water in the river is flowing at 1.0 m/s, how long does it take the boat to make a round trip consisting of a 175 m displacement downstream followed by a 175 m displacement upstream?
Can someone please give me some help in getting this problem started? I've been working on Physics homework for 5 hours now and I feel like my brain is so fried I can't even start this problem (it's my last one). I would appreciate the help!
2007-08-25 15:27:25 · 6 answers · asked by Lisa R 2 in Science & Mathematics ➔ Physics
I got 44.4 s.
I'm embarrassed that it turned out to be so easy. I knew my brain was fried.
2007-08-25 15:46:30 · update #1
Here's help getting started.
Going upstream will slow you down by the amount of the current's speed; going downstream will speed you up by the amount of the current's speed.
Your upstream speed (relative to the bank) is 8m/s–1m/s = 7m/s.
Your downstream speed (relative to the bank) is 8m/s+1m/s = 9m/s
SO:
How long does it take to go 175m at a speed of 7m/sec?
How long does it take to go 175m at a speed of 9m/sec?
Add those two times.
2007-08-25 15:39:02 · answer #1 · answered by RickB 7 · 1⤊ 0⤋
looks like a tricky question, but you're over thinking it. the boat is going 8 m/s relative to the water, so that means if you're on the water the boat seems to pass at 8 m/s. when it goes with the current, it's really going 9 m/s, and against the current 7 m/s. since you're going the same distance against and with the current, it will average out to 8 m/s. so take the total distance (350m) and divide by 8 to get 43.75 seconds. This of course disregards acceleration/deceleration and the time it takes the boat to turn around, but that would be more advanced than the problem seems to call for
2007-08-25 22:39:43 · answer #2 · answered by whatslansing 1 · 0⤊ 1⤋
The key to this problem is the motion of the water. Essentially, the water is moving at a constant speed, like a treadmill. No matter how much you are moving or not, you will be moved by the water at 1m/s. The boat is your runner, he has a maximum speed he can run at, whether it's against or with the treadmill, at 8m/s.
However, we're interested in his displacement relative to the enviroment. So, when you're moving downstream, you're moving at 8m/s 'running' speed + 1m/s for the water, for a sum speed of 9m/s. When you're moving upstream, the current is working against you, so you lose 1m/s to the water and have a sum speed of 7m/s.
The overall travel time is thus the time it takes to cover 175m at 9m/s plus the time it takes to cover the same 175m at 7m/s.
2007-08-25 22:39:40 · answer #3 · answered by Dan 2 · 1⤊ 0⤋
9 m/s downstream, 7 m/s upstream
so: 175/9 + 175/7 = total number of seconds
2007-08-25 22:41:07 · answer #4 · answered by Paladin 7 · 0⤊ 0⤋
The distance is the same each way. Distance = V*t... So,
V1*t1 = 175 and V2*t2 = 175 â9t1 = 175 and 7t2 = 175 from which you get t1 = 19.44 sec and t2 = 25 sec.
Add'em up for the total time of 44.44 sec........
Sleep tite.........
2007-08-25 22:41:09 · answer #5 · answered by Steve 7 · 0⤊ 0⤋
who driving the boat
2007-08-25 22:41:20 · answer #6 · answered by rocketman 3 · 1⤊ 0⤋