The Physics Quiz
The following concerns a question in a physics degree exam at the University of
Copenhagen:
"Describe how to determine the height of a skyscraper with a barometer."
One student replied: "You tie a long piece of string to the neck of the barometer,
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 building."
This highly original answer so incensed the examiner that the student was failed
immediately. He appealed on the grounds that his answer was indisputably correct,
and the university appointed an independent arbiter to decide the case.
The arbiter judged that the answer was indeed correct, but did not display any
noticeable knowledge of physics. To resolve the problem it was decided to call the
student in and allow him six minutes in which to provide a verbal answer which showed
at least a minimal familiarity with the basic principles of physics.
For five minutes the student sat in silence, forehead creased in thought. The arbiter
reminded him that time was running out, to which the student replied that he had
several extremely relevant answers, but couldn't make up his mind which to use.
On being advised to hurry up the student replied as follows:
"You could 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 worked out from the formula H =0.5g x t squared. But bad luck on the
barometer.
Or if the sun is shining you could measure the height of the barometer, then set it on
end and measure the length of its shadow. Then you measure the length of the
skyscraper's shadow, and thereafter it is a simple matter of proportional arithmetic
to work out the height of the skyscraper.
But if you wanted to be highly scientific about it, 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 of the skyscraper. The height is worked out by the difference in the
gravitational restoring force T= 2 pi sqrroot (l / g).
Or if the skyscraper has an outside emergency staircase, it would be easier to walk
up it and mark off the height of the skyscraper in barometer lengths, then add them
up.
If you merely wanted to be boring and orthodox about it, of course, you could use the
barometer to measure the air pressure on the roof of the skyscraper and on the
ground, and convert the difference in millibars into feet to give the height of the
building.
But since we are constantly being exhorted to exercise independence of mind and
apply scientific methods, undoubtedly the best way would be to knock on the janitor's
door and say to him 'If you would like a nice new barometer, I will give you this one
if you tell me the height of this skyscraper.'"
The student was Niels Bohr, the only Dane to win the Nobel Prize for Physics.