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A question of physics, or is it?

Devedander

Active Member
20/10/06
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Devedander said:
Here's another one:

If you drive a 2 laps around a track and the first lap you average 60mph, how fast must you drive the second lap to average 120mph overall speed?


Assume instant acceleration and ability to hold exact speed (thus you can drive exatcly 100mph the whole second lap if you want) to make math easy. It defeats the question to assume weird things like turning around mid lap, artificially extending the track mid race or anything else like that. Assume everthing about lap 2 occurs similar to lap 1 accept your driving speed.

Care to render a guess here Novesh? :)

I like logic puzzles...
 

t185

Known Member
16/1/07
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Heres another one...


Why did the chicken cross the road :?:
 

Novesh

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Devedander said:
Devedander said:
Here's another one:

If you drive a 2 laps around a track and the first lap you average 60mph, how fast must you drive the second lap to average 120mph overall speed?


Assume instant acceleration and ability to hold exact speed (thus you can drive exatcly 100mph the whole second lap if you want) to make math easy. It defeats the question to assume weird things like turning around mid lap, artificially extending the track mid race or anything else like that. Assume everthing about lap 2 occurs similar to lap 1 accept your driving speed.


Care to render a guess here Novesh? :)

I like logic puzzles...

I'm assuming its a little harder than just saying your going to instantly go 180mph for the entire second lap, even though u said to assume.

if we can't assume and everything is relative, you would have to factor in rate of accel and bend of lap (since laps are round) energy out during accel and decel (for overall understanding) and distance of said laps. also what it is your driving, riding, etc...
 

pugwash

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30/4/07
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Devedander said:
Here's another one:

If you drive a 2 laps around a track and the first lap you average 60mph, how fast must you drive the second lap to average 120mph overall speed?
Infinite.

Say it's a 1 mile track, you do that in 1 minute. To do it at 120, you need to do 30-sec a lap, and as you've already used up the minute needed, the remaining lap has to be done in 0 seconds.

Damn, that one actually made me think.
 

Novesh

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t185 said:
Heres another one...


Why did the chicken cross the road :?:

chickens at rest tend to stay at rest, chickens in motion tend to cross roads....
 

Devedander

Active Member
20/10/06
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Novesh said:
Devedander said:
Devedander said:
Here's another one:

If you drive a 2 laps around a track and the first lap you average 60mph, how fast must you drive the second lap to average 120mph overall speed?


Assume instant acceleration and ability to hold exact speed (thus you can drive exatcly 100mph the whole second lap if you want) to make math easy. It defeats the question to assume weird things like turning around mid lap, artificially extending the track mid race or anything else like that. Assume everthing about lap 2 occurs similar to lap 1 accept your driving speed.


Care to render a guess here Novesh? :)

I like logic puzzles...

I'm assuming its a little harder than just saying your going to instantly go 180mph for the entire second lap, even though u said to assume.

if we can't assume and everything is relative, you would have to factor in rate of accel and bend of lap (since laps are round) energy out during accel and decel (for overall understanding) and distance of said laps. also what it is your driving, riding, etc...

You can assume instant accel. Driving a car... no funny business for this one like lack of air resistance or anything, just plane pure math :)

So yes, it's not as hard as you assume, but also no... 180mph for the second lap does not give you a 120mph overall average speed of 120mph :)
 

pugwash

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Devedander said:
You can assume instant accel. Driving a car... no funny business for this one like lack of air resistance or anything, just plane pure math :)
You can also assume I solved it a few posts back. :D
 

Devedander

Active Member
20/10/06
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There is a mountain with a single path spiraling up it.

An old man starts at the base at 7am on the first day and walks up the mountain path arriving at the top at 7pm the same day.

The old man walks at randomly varying speeds and stops for a random number of breaks to rest. Each break is a random amount of time.

The second day the man starts at 7am and works his way down, doing the same thing, and arrives at the bottom at 7pm.

Bearing in mind that the number of breaks, speed he travers and time he spends resting are not necessarily equal or related in any way other than that he gets all the way in 12 hours, is there necessarily a point on day 2 at which he is in the exactly place on the path he was on day 1 at that time of day?

(and by exact I don't mean his feet are in exactly the same spot, but you know, he is at the same place on the path)
 

Devedander

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20/10/06
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Pugwash said:
Devedander said:
You can assume instant accel. Driving a car... no funny business for this one like lack of air resistance or anything, just plane pure math :)
You can also assume I solved it a few posts back. :D

Yes and you can assume I posted another one shortly after :)
 

pugwash

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Devedander said:
is there necessarily a point on day 2 at which he is in the exactly place on the path he was on day 1 at that time of day?
I presume you mean apart from the beginning and the end. If so, then no.
 

Novesh

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ok....I guess I'm missing something

what type of average/mean are you talking about.
 

Devedander

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Actually at the beginning and end he absolutely will not be at the same place at the same time (ie day 2 7am he is at the top and day 1 he is at the bottom and vice versa).
 

pugwash

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Devedander said:
Actually at the beginning and end he absolutely will not be at the same place at the same time (ie day 2 7am he is at the top and day 1 he is at the bottom and vice versa).
Oh, in that case, yes, he has to cross his path at some point. Sorry, I read he went up twice.
 

Devedander

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20/10/06
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Novesh said:
ok....I guess I'm missing something

what type of average/mean are you talking about.

Mean average speed.

ie If you drive 60 miles in 1 hour you averaged 60mph.
 

pugwash

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Novesh said:
ok....I guess I'm missing something

what type of average/mean are you talking about.
Regular average speed. Distance over time stuff.
 

e36wchmstr

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8/5/06
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Haha, what took Devedander less than a page, maybe a full one; took 27 pages on the other board.

That is correct. Jet size is thrust requirements are irrelevant, as given an infinitely long conveyor outdoors any plane should be able to achieve enough lift over a long enough distance to take off.

Now the man, and the car; I'll leave those to you guys.
 

Devedander

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20/10/06
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e36wchmstr said:
Haha, what took Devedander less than a page, maybe a full one; took 27 pages on the other board.

That is correct. Jet size is thrust requirements are irrelevant, as given an infinitely long conveyor outdoors any plane should be able to achieve enough lift over a long enough distance to take off.

Now the man, and the car; I'll leave those to you guys.

What other board? RWG?
 

e36wchmstr

Active Member
8/5/06
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Haha, no not RWG. The board will remain unnamed. 1/2 on the fence one way though, 1/2 on the other. It was never explained until I spoke to an engineer for Boeing personally who happened to come to my shop daily and showed me on paper.
 

pugwash

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e36wchmstr said:
Haha, what took Devedander less than a page, maybe a full one; took 27 pages on the other board.
Yeah but he called me a cheat on RWG for working out how he cheated in the 'triangle' problem. :D