Lets play questions and answers... Some one asks a question and whoever sais the right answer first gets to ask the next question (oh and marks a point... we could make it as a contest)
Wanna try? It'll be cool (I think)

So... first question:
Two camels are galloping towards each other through a desert with a speed of 60 km/h (fast isn't it). A fly keeps flying from the nose of one camel to the nose of the other with a speed of 200 km/h (even faster). Two hours after starting the gallop the camels meet. Each one has passed 120 km. But what distance has the fly flown?
trick question

It's only when you look at an ant through a magnifying glass on a sunny day that you realise how often they burst into flames

If we take our reference coordinate system of observer1 in rest (relative to the earth) at the location of the nose of the one camel the fly is flying away from, he will notice that the nose of the other camel is appoaching the nose of the first camel with a speed of 120 km/h. If the fly approaches the nose of the other camel at 200 km/h, this means the fly is flying at 80 km/h (200-120) km/h for observer2 in a reference coordinate system attached to the first camel (so e.g. an observer on the camel) and thus at 60 km/h + 80 km/h = 140 km/h for observer1. So after two hours observer1 will notice the fly has traveled 280 km with respect to the fly's original position, observer2 will notice the fly has flown 2h*80 km/h = 160 km with respect to the fly's original position while observer3, which we assume in a reference coordinate system on the other camel, will notice the fly has traveled 2*200 km/h = 400 km with respect to the fly's original position.

But your data are actually incomplete. It is not clear what speed the fly is flying in who's coordinate system and whether the distance is with respect to the fly's original position, or observer 1,2 or 3's start or end position. So I made a wild guess and assumed some of these data.

Originally posted by Simon666
But your data are actually incomplete. It is not clear what speed the fly is flying in who's coordinate system and whether the distance is with respect to the fly's original position, or observer 1,2 or 3's start or end position. So I made a wild guess and assumed some of these data.

... and the distance between 2 noses is not provided.

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Originally posted by Simon666
your data are actually incomplete. It is not clear what speed the fly is flying in who's coordinate system and whether the distance is with respect to the fly's original position, or observer 1,2 or 3's start or end position.

The problem clearly states the movement of each animal! Read more carefully. I think you're just saying that because you wanted an excuse for getting it wrong at first . Besides, the coordinate systems were not in the problem, they were created by you.

Originally posted by aio
... and the distance between 2 noses is not provided.

Not necessary.

SolarFlare

Those who cling to life die and those who defy death live. -Sun Tzu

Originally posted by Simon666
If we take our reference coordinate system of observer1 in rest (relative to the earth) at the location of the nose of the one camel the fly is flying away from, he will notice that the nose of the other camel is appoaching the nose of the first camel with a speed of 120 km/h. If the fly approaches the nose of the other camel at 200 km/h, this means the fly is flying at 80 km/h (200-120) km/h for observer2 in a reference coordinate system attached to the first camel (so e.g. an observer on the camel) and thus at 60 km/h + 80 km/h = 140 km/h for observer1. So after two hours observer1 will notice the fly has traveled 280 km with respect to the fly's original position, observer2 will notice the fly has flown 2h*80 km/h = 160 km with respect to the fly's original position while observer3, which we assume in a reference coordinate system on the other camel, will notice the fly has traveled 2*200 km/h = 400 km with respect to the fly's original position.

But your data are actually incomplete. It is not clear what speed the fly is flying in who's coordinate system and whether the distance is with respect to the fly's original position, or observer 1,2 or 3's start or end position. So I made a wild guess and assumed some of these data.

I'll take this for correct. So you get to ask the new question Simon.

It's only when you look at an ant through a magnifying glass on a sunny day that you realise how often they burst into flames

Originally posted by aio
... and the distance between 2 noses is not provided.

Yes it is:

Originally posted by SeventhStar
Two camels are galloping towards each other through a desert with a speed of 60 km/h. Two hours after starting the gallop the camels meet.

That is already enough info.

Originally posted by SeventhStar
Each one has passed 120 km.

Confirms data. I'll try to think of a good question to post.

And about my post, I formulated it rather quickly and thus not entirely clear or correct. I should have stated "with respect to the fly's original position in the reference coordinate system of observerX" to make it more clear.

Originally posted by solarflare
The problem clearly states the movement of each animal! Read more carefully. I think you're just saying that because you wanted an excuse for getting it wrong at first . Besides, the coordinate systems were not in the problem, they were created by you.

The movement of each animal was indeed specified, at least when you consider speed alone a good definition of movement. But speed is always relative to someone. A small example:

Observer1, standing on the earth sees himself as moving with 0 km/h with respect to the earth.

Observer2, sitting in a car sees himself as moving with 100 km/h with respect to the earth in a direction we will assume as the positive X-axis.

Observer3, sitting in a car sees himself as moving with 200 km/h with respect to the earth, in the same direction and sense as Observer2.

The three observers are initially at the same location, which we assume 0 km along the X-axis. The X-axis and origin of all observers coincide at the starting moment. After 1 hour,the situation will be:

Observer1 will notice Observer2 has travelled 100 km and Observer3 200 km.

Observer2 will notice Observer1 has travelled 100 km along the negative X-axis with a speed of -100 km/h with respect to his reference coordinate system and Observer3 has travelled 100 km along the positive X-axis with a speed of 100 km/h with respect to his reference coordinate system.

Observer3 will notice Observer1 has travelled 200 km along the negative X-axis with a speed of -200 km/h with respect to his reference coordinate system and Observer2 has travelled 100 km along the negative X-axis with a speed of -100 km/h with respect to his reference coordinate system.

I've illustrated the following with a figure. Note that:

At the start moment, we assume the location of all the observers is equal.

After one hour, the speeds observed are the same and the distance traveled is always zero to the obsrver in question.

The observer in who's reference system the speeds and location are measured is placed in red.

So, in conclusion, if you say the fly is moving at 200 km/h, you have to say who observes this speed and in who's reference coordinate system you want the distance to be expressed, because otherwise it is open for interpretation.

I interpreted the notion of trick question as that the speed was of 200 km/h was observed by an observer on the camel moving in the opposite direction of the fly in order to obtain a reasonable (=the lowest) speed in relation to an observer on the ground (=140 km/h), and I assumed the distance was to be the distance measured by an observer on the ground also (280 km = 140 km/h*2h).

Originally posted by SeventhStar
Can you get on with question now?

This is a question my professor in Mathematic Analysis asked once at the occasion of 6 december (Saint Nicholas) and the winner received a large piece of chocolate. I didn't solve it as first (no chocolate ) and I do not remember the answer myself. I looked up the question on the internet as I thought it is an existing question. I found it and modified the text a bit:

Someone told his friends that he had 3 daughters. Their ages sum up to the housenumber (13), multiplied the result is 36, and the oldest daughter plays piano. How old are the respective daugthers?

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