Voici la liste des huit problèmes à préparer pour la sélection française de l’IPT 2014.
Pour information, la liste complète des problèmes de l’IPT 2014 est disponible ici.
1. Tagged along
It is well known that in the race cyclists often break up into groups of two or three and tag along with each other in order to minimize air resistance. How much do they benefit from this strategy? Is it useful to marathon runners?
2. High-voltage clock
In the so-called Jacob’s Ladder experiment a spark goes up between two V-shaped electrodes, fades out at the top and burns up again in the bottom.
Evaluate the period of this process given different parameters of the experimental setup. What error will a chronometer have if based on such a device as frequency standard?
Be very careful when working with high voltage!
3. Air Pocket
A stable volume of air can appear near the tap end. That volume increases with time until some moment. After this moment it abruptly decreases. This situation repeats periodically. Explain the phenomenon and find the conditions for it to occur. Find out how the speed of pocket growth and period of oscillations depend on jet parameters.
What is the maximum frequency at which a person can spin a PowerBall? In what way must one rotate the PowerBall so that the energy transfer is the most efficient?
There is a famous experiment where a viscous liquid is placed between the walls of two coaxial cylinders. A drop of ink that is dropped into the viscous liquid can visually be spread apart and gathered back in a drop. Is it possible to carry out this experiment using water between the two cylinders instead and what parameters of the setup should be used?
6. Dry Ball
A ping-pong ball placed over a hair dryer can float in the air, even when the air stream is inclined. What is the biggest angle for which the ball can be in equilibrium?
7. Dangerous flash
In many museums it is prohibited to take photos with a flash. Explain the mechanisms by which a flash can destroy materials. How many flashes does it take to spoil a) medieval icon, b) metal armor, c) papyrus from ancient Egypt? How does the effect depend on flash power?
8. Rubber band ball
How does the “bounciness” of a rubber band ball vary with its size? i.e. for a rubber band ball dropped from a height of 1m, how many rubber bands maximizes the rebound height? The ball must be composed entirely of rubber bands.