Say I go to a fast food restaurant 10 miles away to get lunch. I averaged 29 miles per hour on the way there. Anyway, I need my average speed to be 60 miles per hour for the whole round trip. How fast do I need to go on the way back?
Just say that I got the food in record time so it's negligible and time spent actually traveling is all that matters.
2007-09-22 07:46:07 · 5 answers · asked by Anonymous in Science & Mathematics ➔ Physics
lol. Got one.
2007-09-22 08:09:12 · update #1
time to complete journey: d/v (v is target time)
time you took to complete first leg: d / 2 v1
time remaining: d/v - d / 2v1
distance remaining: d/2
velocity required = distance remaining / time remaining
= d/2 / (d/v - d / 2 v1)
= v1 v / (2v1 - v)
They give you v1 and v. Plugnchug. And you see that....
obviously you need negative velocity to cover the remaining distance in a negative time.
EDIT--asking rhetorical questions just to mess with people--you should have used your Dr.H. troll for THIS one. Of course this is way too difficult to be a Dr H question.
2007-09-22 07:56:38 · answer #1 · answered by Anonymous · 1⤊ 0⤋
If you need to Average 60 mph for the whole trip and you've gone 29 mph for the first half of the trip you need to overcome that low average by going 91 mph on the way back. Chances are you'll be breaking some kind of speed limit.
2007-09-22 14:59:55 · answer #2 · answered by TM 1 · 0⤊ 0⤋
Hehehe. You'll need to -really- haul αss âº
10/29 + 10/v2 = 20/60 equates the times spent to the total time it would take at 60. As you can see, since 10/29 > 20/60 you've already screwed around past the length of time you should have taken to make the trip and return.
You're only hope is to crack lightspeed so that time (you hope) becomes negative âº
Doug
2007-09-22 14:59:33 · answer #3 · answered by doug_donaghue 7 · 1⤊ 0⤋
If you need to average 60mph for a 20 mile trip, you need to make the entire round trip in (20mi)/(60mph) = 20 minutes.
If you average 29 mph for the first 10 mile part, that will take you (10mi)/(29mph) = 20 min, 41 sec.
You blew it. If it takes you 20 min, 41 sec. just to get to the restaurant, there is no way you can make the round trip in 20 minutes!
2007-09-22 15:43:34 · answer #4 · answered by RickB 7 · 1⤊ 0⤋
You won't be breaking any records if Fast food is all you eat.
Well maybe obesity records
2007-09-22 15:29:43 · answer #5 · answered by 4 · 1⤊ 0⤋