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### (5 points)4. Series 27. Year - P. the true gravitational acceleration

Faleš wanted to determine the *gravitational* acceleration from an experiment in Prague(V Holešovickách 2 in the first floor/ground floor). In the experiment he was dropping a round ball from a height of a couple of meters above the Earth. Think about what kind of corrections he had to apply when analysing the data. Then think up your own experiment to determine g and discuss its accuracy.

Karel was thinking about the difference between gravitational acceleration and gravitational force

### (5 points)3. Series 27. Year - P. solar power

Can a plane fly using a solar power?

Dominika with Honza and Michal wanted to fly away to warmer countries.

### (2 points)1. Series 27. Year - 1. golden dam

How many bricks of 24-karat gold can you fit into the Orlík dam? What would be the pressure acting on a brick placed at the deepest point? The dimensions of a brick are 10 cm, 3 cm a 1 cm.

Karel wants to be rich.

### (4 points)5. Series 26. Year - P. Prague is flooded!

In 2002 Prague experienced serious floodings. Try to estimate the amount of water that can fit into the Prague subway system. All the important parameters of the subway system like the train sizes, number of stations, length of the tunnels etc. can be found online.

Karel was drowning.

### (2 points)4. Series 26. Year - 1. Who cares about Einstein?

Who is your favorite physicist except of Albert Einstein? What were her contributions to physics? Why do you consider her to be so brilliant? Why should she be famous? Write a short essay about her life and the discoveries she made.

Karel loves history.

### (5 points)3. Series 26. Year - P. Conspiracy theory?

In this problem you are asked to think about the vapor trails that sometimes form behind an airplane. What are the physical parameters that determine the length of these lines? Estimate and/or find the values of these parameters and determine the range of all possible lengths. Use your results to dismiss the myth of chemtrails that says that these lines are formed by poisonous chemicals being released from the planes.

Michael declared a war on stupidity.

### (8 points)2. Series 26. Year - E. it's fall again

Estimate the average surface area of a leaf of your choice. We are looking forward to see a thorough statistical analysis of your measurements! Use your result to estimate the fraction of energy obtained from the Sun that is used to make saccharides.

### (2 points)1. Series 26. Year - 1. paper

Try to find out dimensions, mass and density of a regular A4 paper (one that you would use in a printer). Given these values estimate its average thickness.

Karel was eating a piece of paper.

### (5 points)1. Series 26. Year - P. airship

What is the minimal wind speed necessary to blow away a paper lying on a flat table?

Karel does not like wind.

### (4 points)6. Series 25. Year - P. x-ray

When you illuminate your fingers with a very intense light in order to see through them, you should notice that you can see individual vessels but the rest seems rather homogeneous. Explain why the vessels are visible but bones are not.

Michal was playing with LEDs.