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### 3. Series 19. Year - P. breathless runner on ice

One winter day Matous went for a run on to frozen fishpond. After several meters he was not able to run any more and he stopped. The ice had broken under him. Explain, why it lasted when he was running!

### 5. Series 18. Year - E. flash-point

Measure the flash-point (the lowest temperature at which the substance ignite) of the refill for the cigarette lighter. As a bonus measure the flash-point for the ethanol or other organic compound.

For example use a resistive wire warmed up by the electric current and let the flow of the gas from the lighter to flow over it. To calculate flash-point use values of the voltage and current and known temperature dependence of the resistivity. Do not restrict yourself to this suggested experiment!

Warning: Fire can cause serious burns, please proceed with extreme caution!

Pavel Augustinský

### 3. Series 18. Year - 1. temperature on the Earth

The average temperature at the earth is $T$ = 287 K. What is going to be the average temperature $T'$, if the average distance between the Earth and the Sun shrinks by 1%?

Část úlohy z 28. MFO v Kanadě.

### 1. Series 18. Year - E. and it spins!

It is few centuries since we know that the Earth spins around its axis. Measure the time, which is needed for the Earth to rotate 360° around its axis. Try to measure with highest possible accuracy. You can suggest and perform more than one experimental method. But, in each case do enough measurements to be able to do some statistic with the results.

Kolektivní výkon.