Easy and happy summer vacation seventh grade national standard version

Let me count how many days 、、、 school starts

I did it so late .........Speechless.........What about the question.........

Answers to summer vacation homework.

24 (6 points) The "Iron and Steel Industry Adjustment and Revitalization Plan" issued in March 2009 proposed that by 2011, China's iron and steel industry should achieve significant results in energy conservation and emission reduction. The comprehensive energy consumption per ton of steel of key large and medium-sized enterprises does not exceed 620 kg of standard coal, the new water consumption per ton of steel is less than 5 tons, the emission of soot and dust per ton of steel is less than l 0 kg, and the carbon dioxide emission per ton of steel is less than l 8 kg.

The density of water is known Water = 1 0x103 kg m3, and the calorific value of standard coal Q = 3 4 107 J kg. Seeking:

1) The volume of 5t water.

2) The heat emitted by the complete combustion of 620kg of standard coal.

25 (6 minutes) As shown in Figure L2, it is part of the circuit of Xiao Li's house, and the lamp L is marked with "220V40W". He inserted an electric kettle with a resistance wire of 40 ohms into an socket and found that it took 5 minutes to boil a full pot of water, and the heat generated by the resistance wire of the electric kettle was 3 105j. If the resistance of the filament and the resistance wire does not change with temperature, find:

1) What is the actual voltage between the live wire and the neutral wire?

2) What is the actual power of lamp L when switch S is closed?

4. Experiment and ** questions (l4 points in total).

26 (6 marks) Figure 13 is the experimental device AB of "How to generate induced current", which is a conductor connected to the two binding posts of the sensitive galvanometer through wires and switches.

1) In this experiment, if so, we assume that there is an induced current.

2) After the switch is closed, if the conductor does not move, the magnet moves horizontally left and right, and the circuit induces current (optionally "Yes" or "None").

3) Xiao Li's experimental team wants to further **"What factors are related to the size of the induced current?" Xiao Li guessed: "It may be related to the speed of the movement of the conductor cutting the magnetic inductance line." ”

Please help Xiao Li design an experiment to test her conjecture according to the experimental setup shown in Figure 13

27 (8 points) In the experiment "What factors are related to the magnitude of friction", an object is pulled at a constant speed in the horizontal direction, and based on the existing knowledge, do you think the reason is:

In the experiment, the students put forward the following conjectures:

a is related to the amount of pressure b is related to the roughness of the contact surface.

c is related to the size of the contact area, d is related to the speed of the movement.

1) Xiao Yang used a long wooden board with a flat surface, a wooden block with a hook and a spring dynamometer to conduct experiments, such as:

Figure 14. The data records he devised are shown in the table below: Counts.