1. Standing on the ground in front of the first carriage of the train, the train moves straight at a constant speed from a standstill. It took him 4s for the first car to pass, and 20s for all trains to pass. (1) How many cars does this train consist of * * * (the length of cars is equal, not counting the distance between cars)? (2) How long did it take for the last nine cars to pass by him?

2. It is known that the density of ice is = 0.9 *10.3 kg/m 3, and water with a volume of 36 cubic decimeters forms ice. How many square meters is the volume of ice?

3. The principle of measuring the density of a substance in the laboratory is _ _ _ _ _. According to this principle, when measuring the density of a liquid, if the measuring cylinder is used to measure the volume first, and then the balance is used to measure the mass, the measured actual value is _ _ _ _ _ _ _ _.

4. Is tension and friction balanced? (Uniform linear motion)

So the force of 16N can make the car move in a straight line at a constant speed. Is the friction 16N?

Can a car move in a straight line at a uniform speed under a force of 22N?

5. The dam will raise the upstream water level and the potential energy of water. When water flows down from the upstream of the dam, it impacts the turbine, and the potential energy of water is finally converted into electric energy.

The Grand Dixon Dam in Switzerland is 284m high, and the dam of Gezhouba Hydropower Station I passed is 70m high. Some people say that the gravitational potential energy of water in the former is greater than that in the latter. Can you draw such a simple conclusion? Why?