# Average speeds

sonhouse
Posers and Puzzles 13 Aug '06 01:22
1. sonhouse
Fast and Curious
13 Aug '06 01:22
So our intrepid hero is in a race and its 1000 Km. He averages only 50 Km/hr in the first 500 Km and he realizes he needs to average 100 Km.hr in the second half to win. So ignoring the acceleration time, how fast does he have to go in the second half to average 100KM/hr?
Xanthos, I did it in my head so I know you can too, so let someone else have a go, ok? I hope you realize that's a compliment.
2. XanthosNZ
Cancerous Bus Crash
13 Aug '06 01:44
Does he need to average 100km/hr for the second half or does he need to average 100km/hr for the entire race to win?

Your question says the first, but that's a stupid problem. If it's the second then you should know that this has been posted multiple times previously.
3. sonhouse
Fast and Curious
13 Aug '06 02:091 edit
Originally posted by XanthosNZ
Does he need to average 100km/hr for the second half or does he need to average 100km/hr for the entire race to win?

Your question says the first, but that's a stupid problem. If it's the second then you should know that this has been posted multiple times previously.
How fast does he have to go in the second half to average 100 Km/hr for the whole race. Its the stupid one.ðŸ™‚
Lets just see who gets it!
4. XanthosNZ
Cancerous Bus Crash
13 Aug '06 02:55
Originally posted by sonhouse
How fast does he have to go in the second half to average 100 Km/hr for the whole race. Its the stupid one.ðŸ™‚
Lets just see who gets it!
"he realizes he needs to average 100 Km.hr in the second half to win."

So he has to average 100km/hr in the second half which he can do by averaging 100km/hr in the second half.
5. abejnood
Independant Thinker
13 Aug '06 04:20
Originally posted by sonhouse
So our intrepid hero is in a race and its 1000 Km. He averages only 50 Km/hr in the first 500 Km and he realizes he needs to average 100 Km.hr in the second half to win. So ignoring the acceleration time, how fast does he have to go in the second half to average 100KM/hr?
Xanthos, I did it in my head so I know you can too, so let someone else have a go, ok? I hope you realize that's a compliment.
Oooh, that was tricky. I was about to post the wrong answer, but after going through it again, the answer is: The speed of light. ( or "impossible to do"ðŸ˜‰

Using the formula d(distance)=v(velocity)/t(time). Substitutuing numbers in, we get t= 10 hours in order for him to finish with average speed being 100KM per hour. However, if you go through it, you realize that it takes 10 sec to go through the first half alone-- leaving zero time for the second half.
6. sonhouse
Fast and Curious
13 Aug '06 04:59
Originally posted by abejnood
Oooh, that was tricky. I was about to post the wrong answer, but after going through it again, the answer is: The speed of light. ( or "impossible to do"ðŸ˜‰

Using the formula d(distance)=v(velocity)/t(time). Substitutuing numbers in, we get t= 10 hours in order for him to finish with average speed being 100KM per hour. However, if you go through it, you re ...[text shortened]... at it takes 10 sec to go through the first half alone-- leaving zero time for the second half.
You got it! Imfrappingpossible! You need to have more than C even, like infinite!
7. XanthosNZ
Cancerous Bus Crash
13 Aug '06 04:59
Originally posted by abejnood
Oooh, that was tricky. I was about to post the wrong answer, but after going through it again, the answer is: The speed of light. ( or "impossible to do"ðŸ˜‰

Using the formula d(distance)=v(velocity)/t(time). Substitutuing numbers in, we get t= 10 hours in order for him to finish with average speed being 100KM per hour. However, if you go through it, you re ...[text shortened]... at it takes 10 sec to go through the first half alone-- leaving zero time for the second half.
Assume he travels at c for the remaining 500km of the race. Then he would have taken 10 hours and 0.000167 seconds to finish the race.

That would give an average speed of 27.778 m/s which is 99.99999954 km/hr. That sthill wouldn't be enough.

Of course here we are applying Newtonian physics to the speed of light which is of course inaccurate.

PS. When doing Physics problems be careful with your units. hours and seconds are definitely not the same thing.
8. sonhouse
Fast and Curious
13 Aug '06 05:101 edit
Originally posted by XanthosNZ
Assume he travels at c for the remaining 500km of the race. Then he would have taken 10 hours and 0.000167 seconds to finish the race.

That would give an average speed of 27.778 m/s which is 99.99999954 km/hr. That sthill wouldn't be enough.

Of course here we are applying Newtonian physics to the speed of light which is of course inaccurate.

PS. W ...[text shortened]... ysics problems be careful with your units. hours and seconds are definitely not the same thing.
Well I guess it wasn't THAT stupid, eh!
Looking at the original posting, it could have been better worded.
It helps to go over these things afterwards it appears.
9. XanthosNZ
Cancerous Bus Crash
13 Aug '06 05:111 edit
Originally posted by sonhouse
Well I guess it wasn't THAT stupid, eh!
You still don't get it do you? Your question was phrased in such a way that the question asked was "What speed does he have to travel in the second half of the race to average 100km/hr in the second half of the race.

Clearly the answer to that question is 100km/hr. That is the interpretation that is stupid. The other interpretation (the one you intended and the only abe answered) is not stupid merely repetitive.
10. sonhouse
Fast and Curious
13 Aug '06 05:29
Originally posted by XanthosNZ
You still don't get it do you? Your question was phrased in such a way that the question asked was "What speed does he have to travel in the second half of the race to average 100km/hr [b]in the second half of the race.

Clearly the answer to that question is 100km/hr. That is the interpretation that is stupid. The other interpretation (the one you intended and the only abe answered) is not stupid merely repetitive.[/b]
Thats what I meant when I re-read it, it was worded wrong. I did not know this kind of problem had been posted here before, show me the link if you will.