physical mechanics

Su Jiaoban eighth grade chapter 8 force unit test paper

Proposer: He Yanchun, chunhui middle school, Temple of Tongshan County.

I. Fill in the blanks (22 points)

1. As shown in Figure 8-2, the football player hit the goal with the header and the ball flew into the net. At this time, the stressed object is _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

2. When people push the cart, the cart changes from static to mobile. This shows that force can change objects.

_______。 The weight is hung under the spring and the spring is stretched. Thus, the force can be shown in Figure 8-2.

Change the _ _ _ _ _ of an object.

3. When screwing a nut with a wrench, we should not only consider the magnitude of the force acting on the wrench, but also consider the sum of the forces, because both will affect the effect.

4. After the ball with a mass of 0.8 kg is thrown, if the air resistance is not considered, the ball will be affected by _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _.

5. At 9: 00 on June 5th, 2003, 10, with the commander's "ignition" order, mega on the Long March launched an orange flame and lifted the Shenzhou 5 spacecraft to the sky. Kinetic energy and gravitational potential energy of Shenzhou 5 spacecraft during its ascent from the ground _ _ _ _ _ _ _ (choose "increase", "decrease" or "unchanged").

6. To stop the bike immediately, you should hold the brake handle tightly, which is increasing the friction of _ _ _ _ _. There are concave and convex patterns on bicycle tires, mainly for _ _ _ _ _ _. Some parts on the bicycle have adopted _ _ _ _ _ and _ _ _ _ methods to reduce friction.

7. As shown in Figure 8-3, the experiment of picking up rice with chopsticks was carried out. Fill the cup with rice, then add a little water and compact it. After a while, chopsticks were lifted, and because of _ _ _ _ _ _, rice and cups were also lifted. The direction of friction on chopsticks is _ _ _ _ _ _.

Second, multiple-choice questions: (2 1)

8. Regarding the concept of force, the following statement is wrong ().

A. Force is the action of objects on objects. Without force, there is no force;

B. the stressed object must also be an applied object;

C. When a force acts, objects must contact each other; Figure 8-3

D. the horse-drawn cart goes forward, and at the same time the cart pulls the horse hard.

9. The weight of the object is about 1N is ().

A. a cow; B. two eggs; C. sewing needles; A TV set.

10. The following statement is true ()

A. The apples on the tree are only affected by gravity when they fall;

B. Waterfalls are formed by water flowing downwards from a height under the action of gravity, and the water surface in the river is flat, so the river is not affected by gravity;

C. When you carry a bucket of water, you will feel the muscle tension in your arm. This is the result of gravity.

D dust suspended in the air is attracted by the earth, and dust also attracts the earth.

1 1. If an object is thrown upward, the following statement is true ().

A. objects move more and more slowly in the process of rising, which is due to the increasing gravity;

B. Objects move faster and faster in the process of falling, which is due to the increasing gravity;

C. When the object rises to the highest point, it is stationary because it is not affected by gravity;

D. during the whole process, the gravity on the object remains unchanged.

12. At present, many countries are developing maglev trains. China's first maglev train test line with completely independent intellectual property rights has been completed, achieving trouble-free operation of 2000 kilometers. Magnets are placed on the carriages and tracks of maglev trains, and most of the magnets used in the carriages are electromagnets with high current. There is the following statement:

① Maglev train is based on the principle that magnetic poles with the same name repel each other.

② Maglev trains use the mutual repulsion of different magnetic poles.

③ The maglev train eliminates the friction between the car body and the track.

④ The maglev train increases the friction between the car body and the track.

The correct combination is ()

A.① and ③ B.① and ④ C.② and ③ D.② and ④

13. Among the following measures, in order to increase friction, it is ().

A. sprinkle some ash on the road in snowy days; B, forming an air cushion between the friction surfaces;

C, smoothing the surface of the sewing needle; D. install the rolling bearing on the machine.

14. At the Olympic Games, "Prince of gymnastics"-Li Ning always put some magnesium powder on his hands before going on the horizontal bar, but he didn't hold the horizontal bar tightly when making a loop on the bar. His purpose is ().

A. The former is to increase friction, and the latter is to reduce friction; B. The former is to reduce friction, and the latter is to increase friction;

C. both increase friction; Both are to reduce friction.

Three. Drawing and experiment: (17 marks)

15. As shown in Figure 8-3, pull the trolley with a force of 40 N and move to the right at an angle of 30 with the horizontal plane. Draw the tension diagram of the car in Figure 8-3.

16. A ball with a mass of 3kg rolls down the inclined plane. In Figure 8-4, the gravity map on the ball is drawn.

17. There is no atmosphere on the moon, and the gravity on objects is 1/6 on the earth. Please talk about what you have learned in physics. What problems do you think should be paid attention to in living and working in this environment, or what different phenomena will happen on earth? Why? Please say 1.

Figure 8-3 Figure 8-4

IV. Calculations and Short Answers (10+10 +20 =40)

18. The mass of a piece of ore measured by a balance is 480.5g.. Q: can you measure its gravity with a spring scale with a range of 0~5 N?

19. The mass of the bottle is 300 g, and the water in the bottle weighs 4.5 N. Find: ① the total mass of the bottle and water; ② Total weight of bottle and water.

20. Read the passage and answer the questions:

After the car brakes

The number of cars in modern society has greatly increased, and an important reason for traffic accidents is that cars can't stop immediately when an accident occurs. It takes a certain time for the driver to operate the brake from seeing the situation to muscle action, which is called reaction time; During this time, the car should keep the original speed for a certain distance, which is called the reaction distance. From operating the brakes to stopping, the car has to travel forward for a certain distance, which is called the braking distance.

(1) When the car runs normally, the friction between the wheel and the ground is _ _ _ _ _.

(2) In order to remind drivers and friends to pay attention to driving safety in rainy and snowy weather, a warning sign "Rain and snow are slippery, slow down" was set up beside the expressway. Please briefly explain the physical reason of this sentence.

Reference answer

1. Player's head, football, football, mutual aid 2. Motion state, shape 3. Direction, action point

4. Earth's gravity, 7.84N, vertical downward 5. Increase, increase 6. Slide, increase pressure, increase friction, replace sliding with rolling, and add lubricant 7. Friction, downward 8.c9.b10.d1.d12.a13.a14.a15 (omitted)/kloc-0.

17.( 1) Pay attention to the problem or phenomenon: when talking directly on the moon, you can't hear the other party's voice. (2) Physical truth: This is because there is no medium for transmitting sound on the moon-air. 18,19,20 (omitted)

I. Fill in the blanks (44 points)

1. The substance is composed of _ _ _ _ _ _

2. When two drops of silver approach, they can automatically combine to form a larger drop of mercury. This fact shows that there is _ _ _ _ _ _ _ _ between molecules, and objects cannot be compressed indefinitely, which means that there is _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

3. The distance between solid, liquid and gas molecules, from large to small, is generally _ _ _ _ _ _ _ _. The order of attraction and repulsion between molecules from large to small is generally _ _ _ _ _ _ _ _ _.

4. "The fragrance of flowers warms people's hearts, and the magpies wear trees to celebrate new feelings." These are two poems in Happy Village written by Lu You, a poet in the Southern Song Dynasty, which describe the beautiful scenery of Chun Qing mountain village with warm climate and flowers. For the previous sentence, from a physical point of view, it can be understood that the aromatic oil secreted by flowers is _ _ _ _ _ _ _ _, which means that the ambient temperature is suddenly _ _ _ _ _ _ _ _ _ _ _ _.

5. The discovery of electrons shows that _ _ _ _ _ _ is separable, atoms are composed of _ _ _ _ and _ _ _ _ _, and nuclei are composed of _ _ _ _ _ _ _ _ _.

6. The sun is _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

2. Multiple choice questions (32 points)

7. The following statement is true ()

A. Open the bottle cap of alcohol indoors. After a while, the whole room smelled of alcohol, which was caused by the movement of alcohol molecules.

Solid molecules, so solid molecules are static.

C. When filing iron parts with a file, many tiny iron powders are obtained, and each iron powder is an iron molecule.

D, intermolecular force is either attraction or repulsion.

8. Solids and liquids are difficult to be compressed, indicating ()

A, intermolecular attraction b, intermolecular repulsion

C, there is no gap between molecules d, molecules have a certain volume.

9. A drop of red ink is dropped into clear water without stirring, and the water turns red after a period of time, indicating ()

A, there is great attraction between ink molecules and water molecules.

B, there is great repulsion between ink molecules and water molecules.

C, ink molecules and water molecules are constantly doing random motion.

D, water is constantly convection.

10. The following statement is wrong ()

A, knead the bread by hand, and the volume of the bread shrinks, which proves that there are gaps between molecules.

B, the liquid enclosed in the container is difficult to be compressed, which proves that there is repulsive force between molecules.

C. After opening the perfume bottle, you can smell the fragrance far away, which proves that the molecules are constantly moving.

D, the coal pile has been in the corner for a long time, and the wall has turned black, which proves that the molecules are constantly moving.

1 1. Among the following statements about intermolecular forces, the correct one is ().

A, an iron bar is difficult to pull off, indicating that there is only a great attraction between the molecules of the iron bar.

B, liquid is easy to flow, indicating that there is only repulsion between liquid molecules.

C the main reason why liquid is difficult to be compressed is that there is only repulsion between liquid molecules.

D, the distance between solid molecules is small, and its molecular force is large.

12. In the following example, it cannot be explained that the molecules are constantly doing random motion ().

First, indoor cleaning, see dust flying in the air in the sun.

B. When drying clothes, the water evaporates and the clothes dry.

C. The sanitary ball is put in the box, and the whole box smells of camphor in a few days.

D. Put a cube of sugar into a glass of boiling water, and the whole glass of water will become sweet in a moment.

13. The reason why ordinary objects are not charged is ()

A, there is no charge in the atom of the object.

B, the positive charge in the nucleus is equal to the negative charge in the neutron band.

C, the neutrons in the nucleus are uncharged.

D, the positive charge of the nucleus is equal to the negative charge of the electrons outside the nucleus.

14. "Copernicus" proposed ()

A, geocentric theory B, Heliocentrism C, BIGBANG D and Xingyun Theory.

Three. Question and answer (24 points)

If the salt molecules are evenly distributed in the large water reservoir of 15.5× 109 m3, how many salt molecules are contained in the water of 1 cm3? What information can you get from the above calculation?

16. In daily life, can you give examples to illustrate the attraction and repulsion between molecules?

17. slowly add a spoonful of sugar to a full glass of water, the sugar melts, and the whole glass of water becomes sweet, but the water will not overflow. Why?

18. Scrape off the wall surface of the corner where coal has been piled for a long time, and you can see that the inside of the wall is also black. Please explain the reason for this phenomenon.

Reference answer

1, molecule,10-10,2, attraction and repulsion, molecules keep moving and decreasing, there are gaps between molecules, 3, gas, liquid and solid; Solid, liquid, gas 4, molecular motion, rising 5, atom, nucleus, electron, proton, neutron 6, galaxy, constant, solar system, travel, earth, satellite 7, A 8, B 9, C 10, A 165438, D/Kloc-. 106, the molecules are very small and numerous, 16, gravity: it is not easy to break an iron bar with great force; Repulsion: Solids and liquids are difficult to be compressed, sugar molecules and water molecules move to each other's gaps, and coal molecules move to the wall.