# 6. Series 21. Year

### 1. free fall of Fykos-bird

A Fykos-bird (the symbol of the seminar) is flying 1 km above the forest at speed 4 m ⁄ s. It is shooted by a men with a gun. The bullet leaves gun at speed 710 m ⁄ s. Our men saw the bird just above his head and fired. How far from him the body of bird will touch the ground? Air friction is negligible.

Vyplodil Honza Prachař.

### 2. cooking in pressure cooker

Assume a pressure cooker, which is filled with half of water and remaining half is filled with air. Then it is closed that no water vapor or air can escape. The cooker with water is slowly heated. At what temperature will water start to boil? What phases are present inside the pressure cooker during increasing temperature?

Sbírka od Dalimila Mazáče.

### 3. cooling a soup

Assume copper hemispherical pot, with diameter of 40 cm. The pot is filled with a soup and is placed in water. It is floating 10cm under water level. Will the water start to fill the pot, if the border of pot is pulled up by a chain by 10 cm?

Sbírka od Dalimila Mazáče.

### 4. quick retreat

Fykos-bird is running through a coridor, which is turning to left. The width of coridor is $b$, bird is running at speed $v_{0}$ and the turn is in distance $d$. If the acceleration will be bigger than $a_{0}$, it will slip and fall down. What is the optimum trajectory to have smallest possible delay?

Napadlo Honzu Jelínka při dobíhání tramvaje za rohem.

### P. mission impossible

Make a plan how to liberate a Fykos-bid from custody. Do not forget to make plan B and C.

Vyplodil Honza Prachař.

### E. magnetic lock

[on request you can get a piece of magnet] Measure the dependence of magnetic force between 2 magnets.

Hint: place a piece of paper between magnets and measure the force needed to separate the magnets.

Vyplodil Honza Prachař.