Eighth grade physics "Pressure and Buoyancy" test questions

1. Multiple choice questions (2 points for each question, ***24 points)

1. A hemispherical container is filled with water. The schematic diagram of the pressure of water on the container wall is shown in Figure 1. The correct one is (Figure 1)

2. As shown in Figure 2, an example of reducing pressure by increasing the force-bearing area is

3. Use a horizontal force F to press the object on the vertical wall, and the object is in a stationary state. When the force F increases, the object still remains stationary, then

A. The gravitational force on the object increases B. The friction force on the object increases

C. The pressure of the object on the wall increases D. The net force on the object increases

4. An object weighing 5N and having a volume of o.4dm3 is thrown into water. If the resistance of water is ignored, when the object is stationary, which of the following statements is correct (g is 10N/kg)

A. The object floats, F float = 5N B. The object floats, F float = 4N

C. The object is suspended, F float = 5N D. The object sinks to the bottom, F floats = 4N

5. The same egg is placed into two cups of salt water of different concentrations, A and B. The egg is in a suspended state in cup A, as shown in Figure 3A; and it is floating in cup B, as shown in Figure 3B. What is certain is that

The density of salt water in cup A is smaller than the density of salt water in cup B

B. The density of salt water in cup A is greater than the density of salt water in cup B

C. The buoyant force on the egg in picture A is smaller than the buoyant force on the egg in picture B

D. The buoyant force on the egg in picture A is greater than the buoyant force on the egg in picture B

6. The two are identical Containers contain two liquids A and B respectively. Two identical small balls are put into the two containers respectively. When the two balls are stationary, the liquid levels are flat and the positions of the balls are shown in Figure 4. , the pressures of two liquids A and B on the bottom of the container are pA and pB respectively, then their relationship is (Figure 4)

A. p Alt; p B B. pA=pB C. pAgt; pB D. Unable to determine

7. As shown in Figure 5, a lead block is hung with a thin line from the bottom of an inflated small balloon. Put it into the water somewhere and it will be in a stationary state. If some water is slowly poured into the pool, the lead block and the air will

A. Still able to stand still B. downward movement c. upward movement D. Stationary, upward or downward movement is possible

8. After heating a flask filled with water until the water boils, remove the flask away from the flame and the water stops boiling. Quickly cork the bottle and turn it upside down. Then pour cold water to the bottom of the bottle (as shown in Figure 6). A large amount of water will immediately be produced in the flask. The reason for bubbles is (Figure 6)

A. The water in the bottle decomposed and produced gas. B. The air pressure in the bottle remains unchanged, the boiling point of the water decreases, and the water boils

C. The air pressure in the bottle increases, the boiling point of water decreases, and the water boils. D. The air pressure in the bottle decreases, the boiling point of water decreases, and the water boils.

9. As shown in Figure 7, it is installed in a connected The left and right water surfaces of the water in the container are level with each other. If a wooden ball is placed in the container on the left, then (Figure 7)

A. The liquid level is higher on the left and lower on the right B. The liquid level is lower on the left and higher on the right

C. The changes in liquid level height on both sides cannot be judged D. The liquid levels on the left and right sides are still equal

10. There is a small hole on the teapot lid. Regarding the function of this small hole, which of the following statements is correct

A. The small hole on the teapot lid is for tying the rope to prevent the lid from being lost

B. The small holes can keep the inside of the pot connected to the outside atmosphere, so that the inside of the pot and the outside world have the same atmospheric pressure, making it easy to pour water

C. The small hole is for making the pot

The internal steam escapes, which is conducive to evaporation and cooling

D. It is a traditional decoration to have small holes on the lid.

11. In winter, after a night of using an open thermos bottle with half a bottle of hot water left, the cork at the mouth of the bottle feels tight when you pull it out the next day. , difficult to pull out, the main reason is ( )

A. The cork expands due to moisture B. The pressure of the gas in the bottle decreases due to the decrease in temperature, and the atmospheric pressure compresses the cork

C. The temperature of the bottle mouth dropped and the cork was sucked in. D. The temperature of the gas inside the bottle dropped and the cork was sucked in.

12. Due to long-term river siltation, the riverbed in the lower reaches of the Yellow River has been raised. Farmers along the river usually use the method shown in Figure 8 to divert water from the Yellow River to irrigate farmland. Regarding this water diversion irrigation method, which of the following statements is incorrect

A. This water diversion irrigation method utilizes the connector principle B. When in use, the pipe mouth at end B must be lower than the water surface at A

C. The pipe must be filled with water before use D. The greater the height difference H, the faster the water flows in the pipe

2. Fill in the blanks (1 point for each remaining blank, *** 12 points)

1. In order to commemorate the outstanding contributions made by physicists, some physical quantities use their names as units. Please choose a physicist in Figure 9: , the unit for which his name is named. (Newton Pascal)

2. In order to make it easier for blind people to walk, blind paths with raised edges were laid on the sidewalks on both sides of the road. Li Gang was walking on the blind path and felt some discomfort in his feet. From a physical perspective, this is because: when walking on a blind path, the ____ ___ between the feet and the ground is reduced, thereby increasing ___ ____.

3. The "Titanic" had discovered the iceberg in front of it before it hit the iceberg and changed its course urgently. However, due to the huge size of the hull, it was difficult for the ship to change its course significantly. One side of the hull still collided with the iceberg, and was hit. After exiting the big hole, water enters the ship, and the total gravity on the ship increases. When the total gravity is buoyant, the ship sinks in the water (select "greater than", "equal to" or "less than").

4. (4 points) Xiao Ming discovered that the amount of force required to open the refrigerator door immediately after closing it is different from that of opening the refrigerator door after a while. Opening the refrigerator door immediately requires less force. He felt strange about this phenomenon. After consulting relevant information, he found out that after closing the refrigerator door, the temperature of the gas in the refrigerator dropped and the gas pressure became smaller. Classmate Xiao Ming understood the reason. Xiao Ming's refrigerator door is 60cm long and 50cm wide. When the atmospheric pressure outside the refrigerator is 1.0×105Pa, the pressure exerted by the atmospheric pressure on the refrigerator door is N. Please cite a similar phenomenon in your life: .

5． A cube placed on the horizontal ground has a gravity of 8×103N and a base area of ??0.4m2. Its pressure on the ground is ___________Pa. If half is cut off in the vertical direction, the pressure of the remaining part on the ground is ___________Pa.

6. On the platform of a subway station, when a train passes by, it will be very dangerous if someone stands within the safety line. This is because when the train is moving, the surrounding air moves, causing the air pressure around the train to ____________. The air pressure outside the human body is ____________ greater than the air pressure inside, which causes danger (fill in "big" or "small")

Three , Experimental investigation (question 1 is 6 points, question 2 is 6 points, question 3 is 6 points, ***18 points)

1. (6 points) Solid cylinder A and cube with the same height Iron block B and cuboid C are placed on a horizontal table as shown in Figure 10. It is known that the cube iron block is the heaviest and the rectangular iron block has the smallest base area. In response to the question "Which of the three iron blocks has the greatest pressure on the tabletop?", the students put forward the following three conjectures:

Conjecture 1: The cube iron block is the heaviest, so it has the greatest pressure on the tabletop.

Conjecture 2: The base area of ??the cuboid iron block is the smallest, so it exerts the greatest pressure on the tabletop.

Conjecture 3: The heights of the three iron blocks are the same, so the pressure exerted by the three iron blocks on the table is the same.

Figure 10

(1) Taking the cuboid C in the figure as the research object, derive an expression for its pressure on the desktop (it is known that the density of iron is ρ, and the cuboid iron The height of the block is h and the base area is S). Determine which of the above conjectures is correct based on the expression.

(2) Using simple equipment such as fine sand, design an experiment to roughly verify the correctness of this conjecture (briefly write down the experimental steps and judgment methods).

Figure 11

2. (6 points) Yang Yang used the pressure gauge shown in Figure 11 to study the characteristics of the internal pressure of the liquid. During the experiment, he removed the rubber membrane of the pressure gauge. Place it in the water at different depths and adjust the orientation of the rubber membrane in the water.

(1) Analyze the table data and fill in the missing data. (2 points)

(2) From experiments 1, 2, and 3, we can draw the conclusion: _______________________________________. (1 point)

(3) From the experiment_______________, it can be concluded that the pressure inside the liquid increases with the depth. (1 point)

(4) Yang Yang wants to complete an experiment to study the relationship between the internal pressure of a liquid and its density. Please help him design a feasible plan. (2 points)

3. (6 points) Xiao Ming uses a spring dynamometer, a metal block, and two identical beakers (containing a certain amount of water and kerosene respectively) to test the The buoyancy force on the object in the object was investigated. Figure 12 shows the exploration process and related data.

(1) Analyze Figures B, C, and D to show that the buoyancy is related to __________________.

(2) The analysis diagram ____________________ shows that the buoyancy force is related to the density of the liquid.

(3) The buoyancy force experienced by an object completely immersed in kerosene is ____________________N.

(4) Xiao Ming also wants to explore whether the buoyancy is related to the shape of the object. Please briefly describe the experimental method.

4. Calculation questions (8 points each, ***16 points)

1. The monument "Blood and Tears Sprinkled Huanghua" (Picture 13) in the alley of Huanghua Road, remember It represents a period of history of Japan's invasion of China and carries a blood debt that Japan owes the Chinese.

The monument is about 1.5m tall, 0.6m wide and 0.1m thick. It is known that the density of the monument is 2.6×103kg/m3. Find: (g in this question is 10N/kg)

(1) What is the weight of the monument? (2) What is its pressure on the ground?

2. Xiao Ming hangs an object on a spring dynamometer and immerses half of the object in a certain liquid. The reading on the spring dynamometer is 4N, and the buoyancy force it receives is 3N. Find the object quality. (g=10N/kg)

Reference answers

1. Multiple choice questions (2 points for each question, ***24 points)

Question number 1 2 3 4 5 6 7 8 9 10 11 12

Answer D C C D A C B D D B D A

2. Fill in the blanks

1. Pascal pressure or Newton force; 2. Force Area pressure; 3. Inertia is greater than;

4. 3×l04 (2 points) Thermos bottle stoppers (can bottle caps, thermos cup caps, cup caps, pressure cookers, etc., 2 points will be given for all reasonable ones)

5. 2×106 2×106; 6. Large reduction;

3. Experimental exploration

1. (1) P＝＝＝＝＝＝ρg h From the above formula, the third conjecture is correct

(2) ① Take a container (such as a sink) and fill it with an appropriate amount of fine sand, shake the sand in the container evenly, Flatten it, gently put the iron block A into the sand, take it out gently after it is still, and measure the depth ha of the sand (or do not take out A, measure the height ha′ of A exposed on the sand surface, then ha = h -ha′; ② In the same way, measure the depth hb and hc of the sand holes generated by B and C in sequence; ③ Compare ha, hb, hc. The deeper the depth, the greater the pressure on the contact surface, which can verify the correctness of the conjecture.

2. (1) 7.5 cm 15cm; (2) At the same depth, the pressure of the liquid is equal in all directions; (3) 1, 4, 5; (4) Omitted

3 . (7 points) (1) Volume of liquid displaced by an object (1 point)

(2) D E (1 point)

(3) 2.4 (1 point)

(4) (The answer is not unique, as long as it is reasonable, both scores will be scored) (2 points)

Experimental method: Experimental equipment: spring dynamometer, a piece of plasticine, a beaker filled with enough water, Thin wire

Steps: 1. Tie the plasticine with a thin wire, hang it on the hook of the spring dynamometer, immerse the plasticine in the water, and read the reading F1 of the spring dynamometer;

2. Knead the plasticine into different shapes, immerse the plasticine in water, and read the indication F2 of the spring force gauge;

3. Compare the sizes of F1 and F2. Draw a conclusion.

IV. Calculation questions

1. Solution:

(1) V =1.5m×0.6m×0.1m = 0.09 m3 ( 1 point)

m =ρV = 2.6×103 kg /m3×0.09 m3= 234 kg (1 point)

G = mg = 234kg×10N /kg = 2340N (1 points)

(2) (Because the stele is placed horizontally and freely) Therefore: F = G = 2340N (1 point)

S = 0.6m×0.1m = 0.06 m2 (1 point )

P = F / S = 2340N/ 0.06 m2 =39000Pa (1 point)

2. (omitted)