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July 22, 2009

Race track problem

A Race track is one mile long, if a driver goes around once at
30 miles per hour, how fast must he drive in the second lap to
average sixty miles per hour over both laps?


Lisa said...

It is impossible for him to average 60 mph over the two laps. He would have to cover the two laps in 2 minutes in order to average 60 mph, but it has already taken him 2 minutes to cover the one lap at 30 mph.

Maria said...

To average sixty miles per hour over both laps he would need to go 90 miles in the second lap.

To make his average speed over the 2 laps = 60 we need
(30 + Lap2Speed)/2 = 60

philofsci said...

Lisa is correct.

In order to average 60 mph (a mile per minute) the driver would need to drive both laps in 2 minutes.

30mph for the first lap means that his first lap took 2 minutes.

Therefore his last lap would have to take no time at all.

Covering any distance in zero time is impossible.

Secret Squïrrel said...

I bet I could cover zero distance in zero time. There... I just did it. And again.

As you and Zeno both know, it is impossible to travel any distance. "I was wrestling with one of Zeno's Paradoxes" is my favourite excuse for being late for an appointment. "I got my arm stuck in the Cornflakes packet" is my second favourite.

Kiklibio said...

buuuuttt... there is a but :D
If you assume you drive a car it isnt possible indeed... but (here is the but :D)
if you drive something that goes
!exactly! the speed of light you can cover the distance in no time :)
if you trave lat the speed of light time stands still :)
goeing faster means you will go "back" in time ;)
its like looking at the stars ;)

just small thing i wanted to add ;)
wonderfull riddle

kind regards

Secret Squïrrel said...

Actually Kiklibio, time only stands still for the person travelling at the speed of light (accepting that something with a non-zero rest mass can actually move that fast which it can't). For the external observer (us with the stopwatch) it will still take some time for the vehicle to travel around the 1 mile track (approx 1/186,000 of a second).

Even if they were to travel faster than light, it will still take some positive amount of time from our perspective to do a lap.

Good lateral thinking, tho'!

Kiklibio said...

Hmm indeed you are right. The external observator will still have a certain time measured. Didn't think of that ^^ thanks

I'm not a fysicist or anything but i love thinking about such things.
Altough i understand the most of what you are saying could you clerify (if you want to ;) ) why a non zero rest mass is needed? i looked the therm "rest mass up" and i think i understand the meaning of it but what are the connections with the speed (of light) ?
How does that influence the measurement?

Thanks for replys :) love to think about these things and learn from them.

Kind regards

Kiklibio said...

ow found a wonderfull site that did the explaining :) I understand it now ^^
thanks anyways :D
I'm getting smarter with the minute :D haha

Kind regards

ashu said...

its impossible
even with d speed of light