[quote=“BigThumb”]A car travels the first kilometer of a two kilometers straigth stretch of road at a speed of 30 km/h. How fast must it travel in the second kilometer to achieve an average speed of 60 km/hour over the whole stretch?
PM the answer and I will post the names of the winning entries so you can feel smart. Contest ends at 10:00 tonight.[/quote]
Over the 2km stretch? I also got 90km/h.
30 + 90 = 120/2 = 60 km/h.
Who knows though. My physics skills are lacking.
yeah but see, it spends less time on the second km stretch as its going faster… haven’t bothered to calculate it, so il guess 120.
To get 60km/hour, you’ll need to calculate the time taken to travel the first stretch, and then figure out the time needed to make the whole thing 60km/hour. But maybe I’m wrong. So algebra time!
Like I already said.
KM1 = 30km/h
KM2 = ? km/h
Average Speed of KM1 + KM2 = 60KM/h
(30 + X)/2 <–divide by 2 to get average = 60 <—X2
30 + X = 120 <---- Minus 30
X = 90 km/h.
If I messed up my physics or my math point it out. Otherwise it’s one of those trick worded questions.
It’s not 90.
If you do 30km/hour in the first bit, you’ll basically be doing 0.5km/minute. Or taking 2 minutes to do one km, right?
Then in the second bit, if you do 90km/hour, you’ll be doing 1.5km/minute, or taking 2/3 minutes (0.6666… minutes) to do the second km.
So in total, you’ve taken 2.66666 minutes to do 2 kms. What does that work out to? Is it 60?
Math hurts my brain.
Hmm, I think 2.6666 km/2 minutes = 45 km/h.
Weird. I think this is one of those “don’t average averages!” questions.
Or one of those questions that you can only answer depending on which physics theory you believe in. 'cause it’s probably impossible 
Since half the distance is already done at 30km/h, it is impossible to do the whole trip at 60km/h, unless you can go infinitely fast.
This is why I am not a math teacher.
Well, I’m going to try attacking it with calculus. But my gut instinct tells me that you would have to go infinitely fast for the second kilometer.
Yeah, that’s what I think too. The faster you go, the quicker you cover the distance, therefore the less of an effect you have on the total average speed.
Well, at 30km/h, it takes you 1/30th of an hour to go 1km. At 60km/h, it takes you 1/30th of an hour to go 2km.
You’ve already used that 1/30th of an hour for the first kilometer, so you have 0 hours to complete the second the kilometer. As speed can be described as distance over time, you’re dividing by a number that approaches zero, so the speed can be said to approach infinity.
Yeah, I’ve thought about it some more, and that’s my answer. Do I win a printer for $20?
Heh, I should have actually read this thread yesterday, instead of just posting random webcomics in it.
Unfortunately, I think I beat you to it. But you can have the printer if you want, and a couple of computers too. Want a laser printer as well?
I’m not sure which one hurt my head more… ME trying to figure out the answer… or watching you guys trying to figure it out.
This is why I gradded with Accounting 11 as my math credit!
Now figure out how to explain this to the wife, that if you spend the alotted time for travelling to Vancouver to visit her Mom pissing at every gas station and stopping for every roadside basket weaver bake sale, there’s no time left to actually travel.
And do it in a way that she won’t be pissed off for a week.
That would be worth a new printer!
And the winner is MiG. You got it right,
[quote] Since half the distance is already done at 30km/h, it is impossible to do the whole trip at 60km/h, unless you can go infinitely fast.
[/quote]
Happy now.
Sorry Eso, you were right but MiG was there first. That’s because you accelerate on Windows while MiG accelerates on Panther.
So geek out on calculus now and tell me if a cop can get an accurate radar measurement on a curve?