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A question in a physics examination at the University of Copenhagen was: "Describe how to determine the height of a skyscraper with a barometer".

One student answered: "You tie a long piece of string to the neck of the barometer and then lower the barometer from the roof of the skyscraper to the ground. The length of the string plus the length of the barometer will equal the height of the skyscraper."

This answer so incensed the tutor that he failed the student. The student appealed to the university on the ground that his answer was indisputably correct. So the university appointed an impartial arbiter, a visiting American professor called Alexandra Calandra, of the University of Washington.

Dr Calandra ruled that although the answer was technically correct, it did not display any noticable knowledge of physics; and to resolve the matter, he called the student in and gave him five minutes in which to answer the question verbally in a way that showed familiarity with the basic principles of physics.

For four minutes there was complete silence. The student sat there frowning, deep in thought. Dr Calandra told him that his time was running out, to which the student replied that he had several relevant answers to the question, nut could not make up his mind which one of them was best.

"You had better hurry up." said Dr Calandra.

"All right then," said the student. "You take the barometer up to the roof of the skyscraper, drop it over the edge, and measure the time it takes to reach the ground. The height of the building can then be calculated in terms of the formula:-

2 H = 1/2gt

(height = one half times gravitational constant times time squared). Unfortunately this procedure might destroy the barometer.

If the sun happens to be shining, you could measure the length of the barometer and then stand it on it's end and measure the length of it's shadow. You could then measure the length of the skyscraper's shadow. It would then be a matter of simple proportional arithmetic to determine the skyscaper's height.

If the skyscraper has an external fire escape, you could walk up it marking off the height in barometer lengths. Then it is simply a matter of counting the marks and multiplying the count by the length of the barometer.

If you wanted to be highly scientific you could tie a short piece of string to the barometer and swing it like a pendulum, first at ground level, and then on the roof, and calculate the height from the difference in gravitational restoring force.

The obvious solution is to measure the barometric pressure at ground level and then on the roof of the skyscraper. You could then convert the difference to metres. However the flaw in this method is that most barometers would have insufficient resolution to accurately detect the difference in barometric pressure over such a relatively small difference in height as is represented by the height of most skyscrapers.

However I really believe that the easiest method would be to go to the caretaker of the skyscraper and say "If you tell me how high the skyscraper is, I will give you this beautiful barometer."

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