1. An important device for raising the national flag at the top of the flagpole is
A. crown block B. moving pulley C. pulley D. labor-saving rod
2. The magical effect of vinegar: it can soften the fish bones-adding a little vinegar when cooking fish can make the fish bones soft and delicious; Peel the egg-add some vinegar to the water before cooking the egg, and it will be easy to peel it after cooking ..... After a bottle of vinegar is half used, the rest is vinegar.
A. the mass, volume and density are all reduced to half of the original.
B, the volume is reduced by half, and the density remains unchanged.
C, the mass is reduced by half and the density is reduced by half.
D. halve the volume and density.
3. Which of the following statements is correct?
A. The portable bucket feels very tired because the gravity of the bucket acts on your hands.
B. The football rolling on the grass will eventually stop because the kinetic energy of the football is exhausted.
C the reason why the shot put can fly in the air is that it is always subjected to thrust.
Team D.A won the tug-of-war because Team A pulled Team B harder than Team B pulled Team A..
4. As shown in figure 1, in order to reduce the pressure, it is
5. The following affiliation is correct.
6. A middle school student climbs from the first floor to the third floor of the teaching building, and the work done by overcoming gravity is the closest.
A.30J B.300J C.3000J D.30000J
7. Xiao Ming puts the densitometer in two different liquids, as shown in Figure 2. If the densities of the two liquids are respectively, and the buoyancy of the densimeter at rest is respectively, then
A.& gt，= B. & lt，& gt
C.& gt，& ltd . >； ,=
8. In the experiment shown in Figure 3, the existence of atmospheric pressure cannot be explained.
9. As shown in Figure 4, the change of mechanical energy of hot air balloon in the following statement is correct.
A kinetic energy decreases, gravitational potential energy remains unchanged, and mechanical energy decreases.
B kinetic energy increases, gravitational potential energy decreases, and mechanical energy decreases.
C when the kinetic energy is constant, the gravitational potential energy decreases and the mechanical energy increases.
D. When the kinetic energy is constant, the gravitational potential energy increases and the mechanical energy increases.
10. Which of the following statements about work, power and mechanical efficiency is correct?
A. A powerful machine must do a lot of work. A fast-moving machine must have high power.
C. efficient machines must have high power. Machines that do more work must be efficient.
As shown in Figure 5, the following statement is incorrect.
A. In Figure A, the bucket leans backward, and the young monk moves his shoulders back a little.
B in figure a, the bucket leans backward, and the young monk moves the bucket behind him forward a little distance.
C in figure b, the young monk moves the bucket forward a little distance to reduce the burden on the old monk.
D. In the second picture, the young monk asked the old monk to move forward a little distance to reduce his burden.
12. As shown in Figure 6, the object A moves in a straight line along the horizontal plane at a speed of 2 m/s under the action of horizontal tension F. At this time, the friction force on the object A is10 n. If the gravity on the pulley and the rope, the friction between the rope and the pulley, and the friction between the pulley and the shaft are ignored, the magnitude and power of the tension force F are respectively
a . 10N 40W b . 5n 10W c . 10N 20W d . 5n 20W
13. Tractors usually walk slowly when plowing in the fields for the following reasons.
A. ensure the quality of cultivated land B. obtain greater traction C. save energy and fuel D. ensure safety
14. as shown in fig. 7, the object a moves from the position of fig. a to the position of fig. b at a uniform speed under the action of horizontal thrust F. in this process,
A.A's pressure on the desktop remains unchanged, and A's pressure on the desktop remains unchanged.
B. A's pressure on the desktop increases, and A's pressure on the desktop increases.
C. the thrust f does work on the object a, but the gravity of the object a does not.
D. The supporting force of the object does not do work on the object, but the gravity of the object does work on it.
15. Put a ruler AB with uniform density on a horizontal desktop, and the part OB of the ruler protruding from the desktop is the full length. When a 5N weight is hung on the B end, the A end of the ruler just begins to tilt, as shown in Figure 8, so the gravity on this ruler is
A.2.5nb.5nc. 10nd。 Can't be sure.
Fill in the blanks (please fill in the correct answer on the horizontal line of the answer sheet, each blank 1 point, * * *1point)
16.5 On June 5, 2009, a sudden landslide occurred in Jiwei Mountain, Iron Mine Township, Wulong County, our city. The landslide involved a wide range, and almost the whole mountain collapsed. The landslide slope is more than 600 meters long and 40 meters high, with an overall slope of more than 45 degrees and a volume of about 1 10,000 cubic meters. In the process of sliding, a lot of energy is converted into energy. At the same time, the landslide could not be stopped immediately, which directly led to the burial of six houses in Sanlian Minefield and opposite the mountain, with huge losses.
17. When exploring the relationship between the mass and volume of two different substances, Xiao Ming got the graph shown in Figure 9. From the figure, we can know that the density ratio of two substances, A and B, is =. If two different substances, A and B, are made into solids with the same mass, their volume ratio is =.
18. As shown in figure 10, the smoke from rural stoves is discharged outside the house along the chimney because the wind blows over the top of the chimney, which makes the airflow speed and pressure there increase.
19. As shown in figure 1 1, there is water in the container, and the pressure generated by water at point A is Pa; If the mass of the container is ignored, the pressure generated by the container on the horizontal plane is Pa (g= 10 N/kg).
20. When coal is left in the corner for a period of time, it is found that the wall turns black, which is a phenomenon, indicating the molecules of solid matter.
2 1. Use a lever to lift an object weighing 200N by 0. 1 m, and under the pulling force of 100N, the direction of the pulling force moves by 0.25 m, so the work done by the pulling force on the machine is the work done by the machine to overcome the resistance, and the mechanical efficiency when using this mechanical lever is.
22. As shown in figure 12, it is our common stapler (staple thick books). The structure and use of stapler apply the physical knowledge we have learned. Please list two places. (Can't repeat with examples)
Example: the elastic potential energy of the spring is converted into kinetic energy to make the stapler reset in time.
( 1)
(2)
Third, the experimental inquiry question (please fill in the correct answer on the horizontal line of the answer sheet, of which 23 is entitled 1, 24 and 25 are entitled 2, ***24. )
23. As shown in Figure 13, Xiaoli puts the pallet balance on the horizontal desktop and moves it to the ruler, and finds that the pointer of the balance refers to the position shown in Figure A. If you want to balance the balance, turn the balance nut on the right (fill in "left" or "right"); Figure B is a scene of correct measurement (below the balance is an enlarged view of the walking scale), so the mass of the object is g. When measuring the mass of another metal block with this balance, use tweezers to take 50 g, 20 g, 10 g and 5 g of 1 weights and put them in the plate on the right, and observe that the pointer is biased to the right. What Xiaoli will do next is: (the minimum weight in the balance box is 5 g)
24. In the experiment of "Exploring the Factors Affecting the Mechanical Efficiency of Pulley", a classmate made three experiments with the same pulley as shown in Figure l4, and the experimental data were recorded as follows:
experiment
Degree hook code
Heavy /n hook code rises
Distance/cm spring dynamometer
On blasphemy number /n spring dynamometer
L/cm distance mechanical efficiency
1 2 8 0.8 24 83.3% 2 4 5 1.5 15 88.9% 3 6 10 90.9%
(1) Fill in the blanks in the form with appropriate data;
(2) The spring dynamometer should be pulled up vertically during the experimental operation;
(3) From the analysis of experimental data, it is concluded that using the same pulley block can improve the mechanical efficiency of pulley block;
(4) The mechanical efficiency of pulley block may also be related to other factors. Please make a wise guess: the mechanical efficiency of pulley block is related to.
Related (write only one influencing factor).
25. Archimedes principle tells us that "an object immersed in a liquid is subjected to upward buoyancy, and the buoyancy is equal to the gravity of the liquid it displaces". Knowing this principle, Xiao Gang thought: Is the buoyancy of an object only related to the gravity of the liquid displaced by the object? So he guessed that the buoyancy of an object may also be related to the density of the object and the depth of immersion in the liquid. In order to verify the conjecture, he selected two solid copper blocks and iron blocks with the same volume and shape for the experiment, as shown in figure 15.
(1) If you want to verify whether the buoyancy of an object is related to the density of the object, Xiao Gang should choose the steps in the figure for comparison. Xiao Gang already knows that the density of copper is greater than that of iron, so we can know the buoyancy of copper (choose "greater than", "equal to" or "less than") and iron according to the readings of spring dynamometer in several drawings he chose. It is concluded that the buoyancy of an object depends on the density of the object (select "relevant" or "irrelevant").
(2) Xiao Gang made a comparative analysis according to the three steps of B, C and D in the figure, and found that the buoyancy of an object increased with the increase of the depth of immersion in liquid, so he concluded that the buoyancy of an object was related to the depth of immersion in liquid. Do you think Xiaogang's conclusion is correct (choose "right" and "wrong") because:
Fourth, discuss the calculation questions (please write the correct answers on the answer sheet, including 26 questions with 9 points, 27 questions with 9 points, 28 questions 12 points, ***30 points).
26. As shown in Figure 16, the trapezoidal cross-section container with a weight of 2 N has a bottom area of 300 cm2, and water with a mass of 4 kg is poured into it, with a water depth of 15 cm. Find:
(1) water pressure at the bottom of the container;
(2) the pressure of water on the bottom of the container;
(3) The pressure of the container on the desktop. (g= 10 Newton/kg)
27. A heavy 10 N solid alloy ball, immersed in water, lined with 4 N water, q:
(1) the volume of the alloy ball;
(2) the buoyancy of alloy balls when they are put into kerosene at rest;
(3) The buoyancy of the alloy ball when it is put into mercury at rest.
(The density of kerosene is 0.8× 103kg/m3, and that of mercury is 13.6× 103kg/m3, taking g = 10n/kg).
28. Use the simple pulley block as shown in Figure l7 to lift the bricks on the construction site. A worker lifted a brick weighing 500 N to the wall 4 meters above the ground at a uniform speed. The pulling force used is 200 N, and the time is 20 s. In this brick lifting process:
(1) The workers have done useful work;
(2) Workers' right to work;
(3) the mechanical efficiency of the pulley block;
(4) Regardless of rope weight and friction, the pulling force used when lifting 800 N bricks with this pulley block at a uniform speed.
Reference answer:
First, multiple-choice questions (3 points for each small question, 30 points for * * *)
The question number is1234567891012131415. Answer ABB BBB BBB BBB.
II. Fill in the blanks (every space 1 minute, *** 16)
16. gravitational potential energy, kinetic energy, inertia (or inertia)
17.2: 1、 1:2
18. Increase and decrease
19.、
20. Diffusion, doing random movements endlessly.
2 1.25J、5J、80%
22. Stapler is a lever with the rotating shaft as the fulcrum. The pressure handle is made wider to increase the stress area to reduce the pressure on the opponent, the base is made wider to increase the stress area to reduce the pressure on the desktop, and the nail tip is made sharper to reduce the stress area to increase the pressure. The force can change the motion state of the object (the answer is reasonable).
Three, experiment and inquiry (***24 points)
23.(4 points) (left) Zero score line, left, 63.4. Subtract 5g from the right side plate, and move the mobile code and its position on the scale.
24.( 10)
( 1)2.2、30
(2) Uniform speed
(3) Increase the weight of hook code
(4) the pulley weight (or friction between machines, automatic rope, etc. )
25.( 10)
(1) A, b, d, e, equal, irrelevant.
(2 points) Wrong, the change of buoyancy when the iron is completely immersed is not considered.
Fourth, the calculation problem. (***30 points)
26.(9 points) (1) (2)4.5N (3)
27.(9 points) (1) (2)3.2N (3) 10N
28. (12) (1) 2000J (2) is about 83.3% (3)300N.