Are there any questions about levers and pulleys?

Compilation of Physics Classification for Senior High School Entrance Examination in p>21-Mechanical, Work and Energy Part

1. Multiple-choice questions

(Lanzhou) 9. As shown in Figure 3, in the process of children sliding down the slide at a constant speed, The following statement is correct (ignoring air resistance)

A. He is influenced by gravity, supporting force, sliding force and friction force

B. He is influenced by gravity, supporting force and friction force

C. His gravitational potential energy is converted into kinetic energy and internal energy

D. His gravitational potential energy is reduced, and kinetic energy is increased. If two objects G1 and G2 are immersed in water at the same time, then

A. The lever can still maintain balance B. The lever cannot be balanced, and the A end sinks

C. The lever cannot be balanced and the B end sinks D. The state of the lever cannot be determined

(Weifang) 6. As shown in the figure, When the ball moves along the track from a standstill to d, air resistance and friction force are ignored. Only kinetic energy and potential energy are transformed into each other. Then

A. The kinetic energy of the ball at A is equal to that at D. B. The kinetic energy of the ball at A is greater than that at D.

C. The mechanical energy of the ball at B is less than that at C. D. The mechanical energy of the ball at B is equal to that at C.

(Suzhou) 12. As shown in the figure. A classmate uses a moving pulley with a weight of 1N to lift a body with a weight of 5N at a uniform speed, excluding friction. Then the possible value of the pulling force F used by this classmate is < P > A.2Nb.25Nc.3Nd.35N < P > (Linyi) 7. The following statement is correct: < P > A. The lever can certainly save energy B. crown block can save energy and change the direction of the force < P > C. The moving pulley can save energy and change the direction of the force D. The pulley country = group both. Put the B end of the centralizer on the ground and keep a certain distance from the root C of the tree by tightening the belt. End a is fixed on the trunk, and a hydraulic device is used to generate a force to push the trunk. Then, when the trunk is righted to the position shown in the figure, point A is pushed in the direction of BA < P > B. It is pushed in the direction perpendicular to AB < P > C. The arm of force is AB < P > D. The arm of force is BC

(Nanchang) 5. The weight A rises at a constant speed in the vertical direction. It is known that the rising speed of the weight A is .2m/s, regardless of the pulley weight, rope weight and friction between the rope and pulley. Then the gravity of the object and the rising speed of the pulley are

a.2n.4m/sb.2n.1m/s

c.5n.4m/sd.5n.1m/s [source: Xueke # net Z#X#X#K]

(Zhenjiang) 12. As shown in the figure. Rope weight and air resistance),

flick the bottom of the test tube upward with your fingers, and the test tube will

a. accelerate upward movement b. decelerate upward movement

c. move upward at a uniform speed d. None of the above statements is true

(Zhanjiang) 11. As shown in Figure 4, Put the wood block beside the compressed spring, release the spring, and the wood block moves to the right along the horizontal ground. After leaving the spring, the wood block moves for a certain distance and stops. The correct statement in the following statement is

A. When the wood block moves, The gravity on the wood block does work for the wood block

B. The elastic force of the spring on the wood block makes the wood block start to move from rest

C. The friction force on the wood block will not change the motion state of the wood block

D. The wood block finally stops moving because of the loss of the elastic force of the spring

(Huanggang) 18. As shown in the figure, there are four ways to lift the same object at a uniform speed with simple machinery (excluding mechanical self-weight and friction). Among them, the least required power is < P > (Huanggang) 19. The following analysis of the process of raindrops falling at a constant speed in the air (regardless of the change of raindrop quality and the buoyancy of raindrops), The correct thing is

A. The raindrop is acted by the balancing force B. The mechanical energy remains unchanged during the raindrop falling

C. The raindrop is subjected to gravity greater than the resistance it receives D. The gravitational potential energy of the raindrop is converted into kinetic energy

(Henan) 14. As shown in Figure 7, with a horizontal pulling force of F=5N, the object A with a weight of 2N moves horizontally to the right at a constant speed by a moving pulley. In this process,

A. Pulling force F did 15J work

B. Pulling force F did 3J work

C. Gravity did 6J work

D. Gravity did 12J work

(Henan) 11. At the party to welcome the Expo, colored balloons rose at a constant speed with the music celebrating. During this process, Mechanical energy increases

C. Kinetic energy remains unchanged, potential energy increases, and mechanical energy increases

D. Kinetic energy remains unchanged, potential energy remains unchanged, and mechanical energy remains unchanged

(Texas) 5. As shown in Figure 3, among the four forces acting at point A, the smallest is

a.f1b.f2

C. When Xiao Juan swings from the highest point on one side to the highest point on the other side, Xiao Juan's

A. Gravitational potential energy keeps decreasing B. Kinetic energy keeps increasing

C. Kinetic energy first decreases and then increases D. Gravitational potential energy first decreases and then increases

(Laiwu) 7. The mechanical efficiency of elevator A is higher than that of elevator B. They respectively lift objects of the same mass to the same height at a constant speed. Then

A. B elevator does more useful work in lifting heavy objects

B. A elevator's motor does more extra work

C. A elevator's motor does less total work

D. B elevator's motor does less total work

(Laiwu) 4. A driver was driving a big truck on a certain road section, and was stopped by the police for speeding. The police said to the driver: The driver said discontentedly, "Why is the speed limit of a car 8 km/h and that of a big car 6 km/h unreasonable!" If you are asked to explain to the driver from a physical point of view, you will tell him that this is because

A. The inertia of an object is related to speed and mass

B. The magnitude of friction is related to speed and mass

C. The kinetic energy of an object is related to speed and mass

D. The magnitude of pressure is related to speed and mass

(Meizhou) 8. In the following process, The gravitational potential energy of an object is transformed into kinetic energy

A. The parachutist falls in the air at a constant speed

B. The hot air balloon ascends

C. The car travels at a constant speed on a level road

D. The shot put falls freely

(Jixi) 12. At the Vancouver Winter Olympics, Li Nina, a player from Heilongjiang Province, won the silver medal in the freestyle skiing competition. The trajectory of her movement during the competition is shown in the figure. If the air resistance is not taken into account, the following statement is correct: ()

A. During the movement from point A to point B, all the gravitational potential energy is converted into kinetic energy

B. At point A and point C, the speed is zero, so the gravitational potential energy is equal

C. During the falling from point C to point D, the gravitational potential energy is converted into kinetic energy

D. At point A. Therefore, the mechanical energy is equal < P > (Jixi) 7. The weightlifting competition requires athletes to hold the barbell above their heads and stay in the air for at least 3 seconds.

in these three seconds,

a. The gravity of the barbell and the supporting force from people are the balancing force ()

b. The gravity of the athlete and the supporting force from the ground are the balancing force

c. The athlete is supporting the barbell forcefully, so he has done work on the barbell

d. The pressure of the barbell on the athlete and the supporting force from people are the balancing force < During a certain operation, the crane used a force of 2N at the free end of the wire rope to lift the goods weighing 6N vertically at a uniform speed for 3m, and then moved it horizontally for 6m. Then in the process of moving goods horizontally, the work done by the gravity of goods is j; In the process of vertically lifting the goods, the work done by the gravity of the goods is J, and the mechanical efficiency of lifting the goods by the traveling pulley block is.

(Zhenjiang) Draw a schematic diagram of the gravity on the object A and the arm of force corresponding to the pulling force F in Figure A.

(Wuhu) 17. crown block is equivalent to a lever when used. As shown in Figure 8, someone pulls the hook code with a rope through the crown block in the oblique direction. It is known that the pulling force of the human hand is F and the gravity of the hook code is G.

(1) Please mark the fulcrum O of this "lever" in the drawing, and draw the pulling force F, the hook code gravity G and their arm of force (keep the drawing trace);

(2) If the friction, pulley weight and rope weight are not taken into account, please use the lever balance condition to deduce: f = g.

(Wuhan) 17. (5 points) The following picture shows the experimental device of Xiaoming's inclined plane mechanical efficiency related to what factors.

In the experiment, he used a spring dynamometer to pull the same block up along an inclined plane with the same roughness to make a uniform linear motion. Some data of the experiment are as follows:

Experiment times

Tilt degree of the slope

Block weight

G/N[ Source: zxxk.com] Slope height

h/m[ Source: Subject Network] Tension along the slope

F/N Slope length

S/M Mechanical efficiency < In the first experiment, the mechanical efficiency of the inclined plane is that the internal energy of the block and the inclined plane is increased by about J.

(2) By analyzing the data in the table, it can be concluded that the steeper the inclined plane is, the higher the mechanical efficiency is. In order to explore the relationship between the mechanical efficiency of inclined plane and the roughness of inclined plane, it should be kept unchanged.

(Zhanjiang) 18. Parabolic phenomenon at high altitude is called "the pain hanging over the city". It is reported that a 3g egg can smash the skull of a pedestrian when dropped from the 18th floor, and people will die on the spot when dropped from the 25th floor. Therefore, the gravitational potential energy of an egg is related to _ _ _ _ _ _ _ _ _, and the falling process is to convert the gravitational potential energy into _ _ _ _.

(Jining). 7. The experimental device of an experimental group to explore the factors affecting the mechanical efficiency of the pulley block is shown in Figure 7, and the experimental data are shown in the following table. If friction is not considered, comparing the experimental data of 1 and 2 times, we can see that the mechanical efficiency of pulley block is related to < P >. Comparing the experimental data of 1 and 3 times, we can see that the mechanical efficiency of pulley block is related to < P >.

(Taizhou). (6 points) When lifting a heavy object with the pulley block shown in Figure 6, it is known that the weight of the object is 2N, and a person pulls the rope downward with a pulling force of 125N, so that the object can rise at a uniform speed of 2m within 5 s. Find:

(1) the work done by the pulling force and the power of the pulling force;

(2) the mechanical efficiency of the pulley block.

(Shanghai) 13. Under the horizontal pulling force of 5 N, if an object moves forward 2 meters along the horizontal ground within 1 seconds, the work done by the pulling force will be _ _ _ _ _ _ _ _ _ _ _ and the power will be _ _ _ _ _ _ _ _ _ _; If the object weighs 2 newtons, the work done by gravity on the object is _ _ _ _ _ _ _ coke.

(Anhui) 8. As shown in the figure, AOB is a simplified schematic diagram of mechanical equipment, and we can regard it as a lever (regardless of its own weight). It is known that AO=2OB. Fix the O point so that the OB is in a horizontal position. At this time, an object weighing 18N is hung on the B end. In order to prevent the lever from rotating, at least a force of F = _ _ _ _ _ N should be applied on the A end, and the direction of the force F at this time should be drawn on the diagram [source: Zxxk.Com]

(Anhui) 21. The rated power of an automobile engine is 6×14W Under the rated power, when the car is driving at a constant speed, find:

(l) the traction provided by the engine;

(2) the driving speed;

(3) The work done by traction after driving for 5min minutes.

(Lanzhou) 33.(6 points) As shown in Figure 23, the weight g is 2N, the slope is 5m long and 3m high, and the total mechanical efficiency of the slope and pulley block device is 8%. If the weight is pulled up along the slope at a speed of .2m/s, find out:

(1) What is the required pulling force F? (2) What is the total power of machinery?

(Chongqing) 21. On the afternoon of January 12, 21, a strong earthquake measuring 7.3 on the Richter scale occurred in the Caribbean island country of Haiti, and the capital Port-au-Prince and most parts of the country were seriously affected. After the earthquake, the international community extended a helping hand and said that it would provide humanitarian assistance to Haiti. During the search and rescue, the Chinese rescue team found that a survivor was blocked in a narrow space by a piece of building material of about 1.8 tons, and the contact area between the material and the ground was about 1.5m2.

(1) What is the pressure of building materials on the ground? (g = 1N/kg)

(2) Due to the limitation of conditions, the rescue team can only lift the building materials with the pulley as shown in Figure 17. If the mechanical efficiency of the pulley block is 8% in the lifting process, find the pulling force exerted by the free end of the rope in this process.

(3) If the upward speed of the material is .1m/s when the material is pulled, what is the power of the pulling force?

(Huanggang) 24. The picture on the right shows the escalator of a shopping mall. Some geometric dimensions of the escalator are shown in the figure. Xiaohua, with a mass of 5kg, stands on the escalator from the first floor to the second floor of the shopping mall. It is known that the escalator moves upward at a uniform speed of 1m/s.. The work done by the escalator to him is _ _ _ _ _