First, multiple choice questions
(Lanzhou) 9 As shown in Figure 3, in the process of children sliding down the slide at a uniform speed, the following statement is correct (ignoring air resistance).
A. He is influenced by gravity, support, sliding force and friction.
B.he is influenced by gravity, support and friction.
C. His gravitational potential energy is converted into kinetic energy and internal energy.
D. His gravitational potential energy decreases, his kinetic energy increases, and his mechanical energy remains unchanged.
(Lanzhou) 12. As shown in fig. 5, objects G 1 and G2 with the same volume are hung at both ends of the lever respectively, and the lever is in a balanced state. If two objects G 1 and G2 are immersed in water at the same time, then
A. the lever can also maintain balance. B. the lever can't be balanced, and the A end sinks.
C. the lever can't be balanced, and the B end sinks. The state of the lever cannot be determined.
(Weifang) 6. As shown in the figure, when the ball moves along the track from the static state to D, the air resistance and friction are ignored.
Force, only kinetic energy and potential energy are transformed into each other.
A. the kinetic energy of a ball at point a is equal to that at point d.
B. the kinetic energy of the ball at point a is greater than that at point d.
C. the mechanical energy of the ball at point b is less than that at point C.
D the mechanical energy of the ball at point b is equal to that at point C.
(Suzhou) 12. As shown in the figure, a classmate uses a moving pulley with a weight of 10N to lift an object with a weight of 50N at a constant speed.
Body. Excluding friction, the possible values of tension F used by this student are
20n 25n c 30n d 35n
(Linyi) 7 The following statement is correct.
A. leverage can save labor. B. The crown block can save labor and change the direction of force.
C. moving pulleys can save energy and change the direction of force. D. pulley countries can save energy and change the direction of force.
(Quzhou) 17. The picture shows a tree centralizer. Put the B end of the centralizer on the ground, and keep a certain distance from the root C by tightening the belt. The A end is fixed on the trunk, and a hydraulic device is used to generate the force to push the trunk. Then, when the trunk is restored to the position shown in the figure, the point A of the trunk
A. being pushed in the direction of BA
B. pushed in the direction perpendicular to AB.
C. the arm of thrust is AB.
D. the arm of thrust is BC.
(Nanchang) 5 As shown in Figure 4, under the vertical force F of 10N, the weight A rises at a constant speed in the vertical direction. It is known that the rising speed of the weight A is 0.2m/s, regardless of the pulley weight, rope weight and friction between the rope and the pulley, the gravity of the object and the rising speed of the pulley are respectively
A.20N 0.4m/s B.20N 0. 1m/s
C.5n0.4m/SD.5n0. 1m/s [source: Xue # ke # net Z#X#X#K]
(Zhenjiang) 12. As shown in the figure, the hook yard and the test tube filled with water are at rest on both sides of the crown block (regardless of friction, rope weight and air resistance).
Tap the bottom of the test tube with your finger. After the test tube leaves your finger and before touching the crown block, the test tube will
A. upward acceleration movement B. upward deceleration movement
C. move up at a constant speed D. none of the above statements are correct
(Zhanjiang) 1 1. As shown in Figure 4, put the wooden block next to the compressed spring, release the spring, and the wooden block moves to the right along the horizontal ground. After leaving the spring, the block moves for a certain distance and then stops. The following statement is correct.
A. When the block moves, the gravity exerted on the block does work.
B, the elastic force of the spring on the block makes the block move from the static state.
C. the friction on the block will not change the motion state of the block.
D. the stone finally stopped moving because it lost the elasticity of the spring.
(Huanggang) 18. As shown in the figure, there are four ways to lift the same object with simple machinery at a uniform speed (excluding mechanical self-weight and friction), among which the minimum power required is
(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) is correct.
A. raindrops are subjected to a balancing force. B. the mechanical energy will not change during the raindrop falling.
C. the gravity of raindrops is greater than the resistance. D. the gravitational potential energy of raindrops is converted into kinetic energy.
(Henan) 14. As shown in fig. 7, under the condition of horizontal pulling force F=50N, the object A with a weight of 200N moves horizontally to the right at a uniform speed of 3m, during which.
A. the pulling force f has done work of 150J.
The pulling force f is 300 joules.
C. gravity did 600J J j.
D. gravity has done work of1200 j.
(Henan) 1 1. At the party to welcome the World Expo, colored balloons rose at a constant speed with the music of celebration. In the process, the balloon
A. kinetic energy is converted into potential energy, and mechanical energy remains unchanged.
B. kinetic energy is converted into potential energy, and mechanical energy is increased.
C. kinetic energy is constant, potential energy increases, and mechanical energy increases.
D. kinetic energy is constant, potential energy is constant, and mechanical energy is constant.
(Texas) 5. As shown in Figure 3, in order to make the lever in a balanced state, the smallest of the four forces acting on point A is
A.F 1 B.F2
C.F3 D.F4
(Texas) 1. Swing is a common entertainment and leisure activity, and it is also a competition in the National Games of China. When Xiao Juan swings, in the process of swinging from the highest point on one side to the highest point on the other side, Xiao Juan's
A. the gravitational potential energy is decreasing. B. the kinetic energy is increasing.
C. kinetic energy first decreases and then increases. D. the gravitational potential energy first decreases and then increases.
(Laiwu) 7. The mechanical efficiency of elevator A is higher than that of elevator B. They lift objects of the same mass to the same height at a uniform speed. rule
A. elevators do more useful work to lift heavy objects.
B. the motor of elevator a does more extra work.
The motor of elevator A does less total work.
D. the motor of elevator b does less total work.
(Laiwu) 4. A driver is driving a big truck on a certain section. He was stopped by the police for speeding. The policeman said to the driver, "Sir, your speed just now was 70 km/h, which is speeding." The driver said discontentedly, "Why is the speed limit of cars 80km/h and that of big cars 60km/h unreasonable?" If you explain to the driver from a physical point of view, you will tell him that this is due to
A. the inertia of an object is related to speed and mass.
B. the magnitude of friction is related to speed and quality.
C. the kinetic energy of an object is related to speed and mass.
D. pressure is related to speed and quality.
(Meizhou) 8. In the following process, the gravitational potential energy of an object is converted into kinetic energy.
A. the process of paratroopers falling at a constant speed in the air
B. the process of hot air balloon ascending
C. the process of the car driving at a constant speed on a horizontal road.
D. the process of free fall of shot put
(Jixi) 12. At the Vancouver Winter Olympics, Li Nina from Heilongjiang Province won the silver medal in freestyle skiing. Her movement track during the competition is shown in the picture. If you don't count the air resistance, the following statement is correct ().
A. During the movement from point A to point B, all gravitational potential energy is converted into kinetic energy.
The velocity of point A and point C at point B is zero, so the gravitational potential energy is equal.
C. in the process of falling from point c to point d, gravitational potential energy is converted into kinetic energy.
D both point a and point e are stationary, so the mechanical energy is equal.
(Jixi) 7. The weightlifting competition requires athletes to hold the barbell above their heads and remain still in the air for at least 3 seconds.
In these three seconds,
A. The gravity of the barbell and the supporting force of people are the balance force ().
B. the gravity and ground support on the athlete are the balance force.
C. The athlete is trying to support the barbell, so he has done some work on it.
D. the pressure of barbell on athletes and people's support for it are both balancing forces.
Second, fill in the blanks and experiment questions
(Wuhu) 9 Figure 5 shows the pulley block used to lift goods in the factory. In an operation, the crane used the force of 2000N at the free end of the wire rope to lift the goods weighing 6000N vertically at a constant speed for 3m, and then moved horizontally for 6m. Then in the process of moving the goods horizontally, the work done by the gravity of the 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 walking pulley block is.
(Zhenjiang) Draw the gravity diagram of the object A and the arm L corresponding to the pulling force F in Figure A. 。
(Wuhu) 17. The crown block is equivalent to a lever when used. As shown in Figure 8, someone pulled the hook code with a rope obliquely through the crown block. It is known that the pulling force of human hand is f and the gravity of 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 its arm of force (keep drawing traces);
(2) If friction, pulley weight and rope weight are not considered, please use lever balance condition to prove that f = g. ..
(Wuhan) 17. (5 points) The following figure shows the experimental device with which the mechanical efficiency of Xiaoming inclined plane is related.
In the experiment, he used a spring dynamometer to pull up the same building block along an inclined plane with the same roughness to make a uniform linear motion. Some data of the experiment are as follows:
experiment
angle of inclination
Inclination, block weight
G/N[ Source: zxxk.com] Slope height
H/m [Source: Subject Network] Tension along the inclined plane
F/n slope length
Efficiency of surveying and mapping machinery
1 slow 10 0. 1 5.0 1
2 steep 100.36.7 145%
3 steepest 10 0.5 8.4 1 60%
(1) Xiaoming explores the relationship between mechanical efficiency and slope. In 1 experiment, the mechanical efficiency of inclined plane is that the internal energy of block and inclined plane increases by about J.
⑵ By analyzing the data in the table, it can be concluded that when the slope roughness is the same, the steeper the slope, the higher the mechanical efficiency. In order to explore the relationship between slope mechanical efficiency and slope roughness, 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 30g egg falling from the18th floor can smash the skull of pedestrians, and people who fall from the 25th floor will die on the spot. It can be seen that the gravitational potential energy of eggs is related to _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _.
(Jining) .7. The experimental device of an experimental group to explore the influencing factors of pulley block mechanical efficiency is shown in Figure 7, and the experimental data are shown in the following table. If the friction is excluded, we can see that the mechanical efficiency of pulley block is different from that of pulley block by comparing the experimental data of 1 and twice.
Correlation; Comparing the experimental data of 1 and 3 times, it can be seen that the mechanical efficiency of pulley block is different from that of pulley block.
Related.
(Taizhou). (6 points) Use the pulley block shown in Figure 6 to lift heavy objects. It is known that the weight of the object is 200N, and people can pull the rope downward with the pulling force of 125N, which can make the object rise at a uniform speed of 2m within 5 s.
(1) tension and the work done by the power of tension;
(2) Mechanical efficiency of pulley block.
(Shanghai) 13. Under the horizontal tensile force of 5 N, if an object moves 2 meters along the horizontal ground within 10 second, the work done by the tensile force is _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ watts; If the object weighs 20 Newton, the work done by gravity on the object is _ _ _ _ _ _ _ _ _.
(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 40N is hung at the B end. To prevent the lever from rotating, at least a force F = _ _ _ _ _ N should be applied at the A end, and the direction of the force f should be drawn on the drawing [source: Zxxk]. Com】。
(Anhui) 2 1. The rated power of the automobile engine is 6× 104W, and the resistance is 1800N when driving at a constant speed on a horizontal road. Under the rated power, when the car is driving at a constant speed, it is found that:
(l) The traction provided by the engine;
(2) 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 2000N, the inclined plane is 5m long and 3m high, and the total mechanical efficiency of the inclined plane and pulley block device is 80%. If the weight is pulled up along the inclined plane at a speed of 0.2m/s, find:
(1) What is the required pulling force f? (2) What is the total power of machinery?
On the afternoon of 2 1 (Chongqing) and 201kloc-0/2 (local time) in the Caribbean island country, strong earthquakes measuring 7.3 on the Richter scale occurred, 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 process, the Chinese rescue team found that a survivor was blocked in a narrow space by a 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 = 10N/kg)
(2) Due to conditions, the rescue team can only use the pulley as shown in Figure 17 to lift the building materials away. If the mechanical efficiency of the pulley block is 80% in the process of lifting, find the tension exerted by the free end of the rope in this process.
(3) If the upward velocity of a substance is 0.0 1m/s when it is pulled, what is the pulling power?
(Huanggang) 24. The picture on the right shows the escalator in a shopping mall. The figure shows some geometric dimensions of the escalator. Xiaohua, weighing 50kg, is standing on the escalator from the first floor to the second floor of the shopping mall. It is known that the escalator runs upward at a constant speed of 1m/s ... then the work done by the escalator to him _ _ _ _ _ _ _ _ _ J, and the work done to him is _ _ _ _ _ w. If the number of people standing on the escalator increases, the efficiency of the escalator is _ _ _ _ (fill in "bigger" and "smaller" Huawei will be faster if it is small.
(Huanggang) 25. The picture on the right shows the road drilling rig (commonly known as "woodpecker") commonly used in road maintenance. This machine uses compressed gas to push the piston and drive the drill bit into the road. When the gas pushes the piston, It can be converted into _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ If its mechanical efficiency is 40%, the useful work done by complete combustion of 50 kg diesel oil _ _ _ _ _ _ j (the calorific value of diesel oil is 4.3× 107 j/kg).
(Suzhou) 26. (8 points) As shown in the figure, the length of the inclined plane is S= 10m and the height is H = 4m. Thrust f along the slope, a heavy one
An object of 100N is pushed from the bottom to the top of the inclined plane A at a uniform speed, and the object overcomes the friction force during the movement.
Did the work of 100J. Find:
(1) Work done by an object to overcome gravity in the process of motion;
(2) the mechanical efficiency of the inclined plane;
(3) The magnitude of thrust f 。
(Yancheng) 16. In the experiment of exploring the lever balance condition, if the right side of the lever is higher than the left side,
● The balance nut on the left side can be lifted and adjusted to be in the water.
Close the balance. As shown in the figure, hang 3 at the scale of 20cm on the left side of the fulcrum.
On the scale on the right side of the fulcrum 15cm, put a hook code with a weight of 0.5N every time.
The spring dynamometer pulls the lever to balance it horizontally. Make the spring dynamometer display
Minimum number, the tension of the spring dynamometer should be along this direction, and then read it.
The number is n.
(Yancheng) 20. Workers use the crown block to lift an object with a weight of 240N at a uniform speed. The tension used is 250N, and the weight rises by 4 m in 5 s. 。
In this process, the useful work is ▲ J, and the power of pulling work is ▲ W. Write a reason why the pulling force is not equal to the weight of the object:
(Quzhou) 26. In the Zhejiang Pavilion of the Shanghai World Expo, there is a "celadon giant bowl" with a diameter of 8 meters, which contains 6 tons of "water". Under the light, the blue waves rippled in the celadon bowl, accompanied by the melodious sound of silk and bamboo, and tourists seemed to be in the picturesque south of the Yangtze River.
(1) Tourists see the rippling "water" surface because it faces the light.
(2) Around the "celadon giant bowl" is a huge annular lifting platform. Visitors stand in a circle on the lifting platform. After the lifting platform rises, they can see the inside of the celadon giant bowl at the same time. In a certain lifting, the lifting platform raised 80 tourists by 3 meters at a uniform speed. If the mass of each tourist is calculated as 60 kg, then the work that the lifting platform does for tourists in this lifting process is ▲ Coke.
(Xianning) 13. During the exercise as shown in Figure 5, the mass of object A is 4kg, excluding pulley friction. When swinging the ankle downward so that the object A pulled by the string rises slowly (at a uniform speed), the pulling direction of the ankle on the string is changing, and the magnitude is also changing (select "also changing" or "unchanged"). If the ankle lifts the object A 0.3m at a uniform speed within 2.4s, the work done on the object A is J and the power is W. ..
(Xianning) 14. Pole vault is a high-tech sport, and the whole process can be simplified into three stages as shown in Figure 6: holding the pole to run up, lifting the pole and dropping the pole. In the process of reaching the highest point, kinetic energy is converted into; It can be gradually increased during the decline.
(Suqian) 23 A reporter reported that in the Botanical Garden, he saw an old man reaching for a piece of wood with a length of about 3m and a radius of about 0.2m, and gently lifting it on his head to enjoy himself. As shown in Figure A, this kind of wood is the lightest wood on the earth-balsa wood, with a density of 0.2g/cm3 (g = 10n/kg).
Please calculate and answer whether the above report is true through the data given in the article.
(2) If the wood is placed vertically on the horizontal ground as shown in Figure B, find its pressure on the ground;
(3) If the pulley block shown in Figure C is used to hoist the wood to the car at a uniform speed, the pulling force F used is 3 14N ... Find the mechanical efficiency of the pulley block.
(Nantong) 32. (8 points) As shown in the figure, the master uses the crown block and the movable pulley to form a pulley block, and lifts the box weighing 500N at a uniform speed for 5m, with the mass of the movable pulley of 8kg, taking g = 10N/kg, regardless of rope weight and friction.
(1) The pulley block in the drawing is assembled with lines instead of strings.
(2) In the process of lifting the box upwards, what is the pulling force of people on the rope?
(3) What is the mechanical efficiency of the pulley block during the upward lifting of the box?
Zhanjiang, 23. A stevedore in Zhanjiang Port uses a pulley block as shown in Figure 1l to lift the cargo with a mass of 80 kg at a uniform speed, and the pulling force F used is 500N, and the free end of the rope is pulled down at a uniform speed of 4m within 50s, so: (g is 10N/kg).
(1) Before lifting, the goods are still on the ground, and the contact area with the ground is 0.04m2 Find the pressure of the goods on the ground.
(2) the speed of the free end of the rope in the process of lifting.
(3) The power of pulling force F 。
(4) the mechanical efficiency of the pulley block.
40.(5 points) Sports activities also contain a lot of physical knowledge. The following table shows the results of a sports test in Yang Wei.
Please make the following calculation according to the information provided in the table: (g is 10N/kg)
(1) What is the average speed of Yang Wei 100m?
(2) In figure 14, Yang Wei's weight is 500N, and point A is the center of gravity. Please calculate the supporting force f according to the data in the figure;
(3) Yang Wei lifted the barbell for 2m in 4s, so what was his motivation for lifting the barbell?
(Texas) 15. As shown in fig. 22, rope weight and friction are not included. The stevedores hoisted the cargo weighing 800N to a high place, and the pulling force of people on the rope F 1 was 500N, and the cargo rose at a constant speed within 1min.
(1) Please draw the winding method of the rope on the diagram;
(2) Find the mechanical efficiency of the pulley block;
(3) If the weight is 600N, lift the weight for 5m and find the work done by the pulling force.
(Meizhou) 16. As shown in Figure 5, it is an experimental device for measuring the mechanical efficiency of pulley blocks, with a total hook weight of 6N. During the experiment, the spring dynamometer should be pulled vertically and upwards at a uniform speed. As can be seen from the figure, the pulling force is n, and if the hook height is 8cm, the spring dynamometer moves up by cm, and the mechanical efficiency of the pulley block is% (the result remains one decimal place).
(Meizhou) 26. As shown in figure 14, the mass of object a is m = 12kg. Under the action of the pulling force F, the object A moves in a straight line on the horizontal plane at a speed of 0. 1m/s, and the pointer of the spring dynamometer is 12N, ignoring the friction between the pulley and the rope, and the friction between the pulley, the spring dynamometer and the rope. Q:
(1) The magnitude of the friction force f between the object A and the horizontal plane;
(2) the magnitude of the pulling force f;
(3) The work done by the pulling force F to 10s during the movement of object A..
(Jixi) 25. There is a scene in the TV series "Three Kingdoms" in which a group of soldiers pull a lever and throw stones at the enemy camp. This is a lever. When throwing a stone, the force acting on point A in the figure is the smallest in the direction (fill in A, B or C).
(Jixi) 33 In order to get good grades in the physical examination of the senior high school entrance examination, Xiaoyu does physical exercise every day.
(1) first jogged along the 200m track, and ran 12 laps from 6: 00 to 6: 10 * *. What is his average speed?
[Source: Xue. Ke. Net]
(2) Start skipping rope after jogging. If Xiaoyu's weight is 60kg and the take-off height is about 5cm, how much coke does he need to overcome gravity every time he takes off?
(3) In the "1 minute jump rope" test of the senior high school entrance examination, Xiao Yu jumped 160 times and Xiao Ming jumped 100 times. Question: Do students with good grades work hard in the exam? State your reasons.
Work and mechanical energy 2
13.(20 10, Guangzhou, 4 minutes) Party A stands on the escalator with a constant speed of 0.5m/s, and Party B stands on the escalator with a constant speed of 0.7m/s, with the same mass of Party A and Party B, and Party A has rising kinetic energy (select "increase",
"constant" and "decrease"). Their positions at a certain moment are shown in figure 13.
At this time, the gravitational potential energy of a, the gravitational potential energy of b, and the machine of a.
Mechanical energy Mechanical energy B. (Choose "greater than", "equal to" and "less than"
If the ascending escalator suddenly stops moving at this time, A will lean forward.
The reason is.
Answer: 13. The constant is equal to or less than the friction of the nail foot and stops immediately, while the upper body continues to move forward due to inertia.
20.(20 10, Guangzhou, minutes) As shown in Figure 23 (pulley block winding is not shown), a person pulls down one end of the rope wound on the pulley block with a force of 600N for 10 second, so that the end of the rope moves down 1.5m, and the weight rises at a constant speed.
When the length of pulley block is 0.5m, the mechanical efficiency of pulley block is 70% (g = 10N/kg).
(1) What is the strength of human pull?
(2) What is the weight of the lifted weight?
(3) Draw the winding rope of pulley block according to the meaning of the question.
2 1.(20 10, Anhui, 8 minutes) The rated power of the automobile engine is 6× 104W, and the resistance when driving at a constant speed on a horizontal road is 1800N. Under the rated power, when the car is driving at a constant speed, it is found that:
(l) The traction provided by the engine;
(2) speed;
(3) The work done by traction after driving for 5min minutes.
Answer: 2 1. (1) Traction force F =f= 1800N (2 points) Because the car is driving at a constant speed, it is affected by the balance force.
(2) From P=Fυ, it can be concluded that the uniform running speed of steam cattle υ = p/f = 6×104 w/1800n = 33.3 m/s (3 points).
(3)w = Pt = 6× 104 w×5×60s = 1.8× 107j
5.(20 10, Anhui, 2 points) Now earthquakes happen from time to time, so people begin to pay attention to the reinforcement and maintenance of houses, and we can often see pictures and pictures. If workers slowly hoist 50 "cement to the roof with pulleys, the pulling force used is about 300N, and the efficiency of this machine is about _ _ _ _ _ _ _.
.7, (20 10, Jining, 2 points) The experimental device of an experimental group to explore the influencing factors of pulley block mechanical efficiency is shown in Figure 7, and the experimental data are shown in the following table. If the friction force is excluded, we can see that the mechanical efficiency of the pulley block is the same as that of 1 and 2 times of experimental data. Comparing the experimental data of 1 and 3 times, we can see that the mechanical efficiency of pulley block is different from that of.
7.(20 10, Chengdu, 2 points) As shown in Figure 2, it is the first "Oriental Crown" in China Pavilion of Shanghai World Expo. During a visit, Mr. Li went upstairs by elevator. In the process of the elevator rising at a constant speed, Mr. Li's
A. kinetic energy is increasing.
B. the gravitational potential energy is increasing.
C. conversion of kinetic energy into gravitational potential energy
D, converting gravitational potential energy into kinetic energy.
20.(20 10, Chengdu, 4 points) In physics, it is necessary to introduce different physical quantities to compare different things. For example, to compare the speed of object movement, we must introduce speed; To compare the speed of work, it is necessary to introduce it; In order to compare the effect of stress, it is necessary to introduce it.
26.(20 10, Suzhou, 8 points) As shown in the figure, the length of the inclined plane is S= 10m, and the height is H = 4m. Thrust f along the slope, a heavy one
An object of 100N is pushed from the bottom to the top of the inclined plane A at a uniform speed, and the object overcomes the friction force during the movement.
Did the work of 100J. Find:
(1) Work done by an object to overcome gravity in the process of motion;
(2) the mechanical efficiency of the inclined plane;
(3) The magnitude of thrust f 。
20.(20 10, Suzhou, 3 points) A construction worker pushed the trolley with a horizontal thrust of 50N, which made the trolley advance at a constant speed of 1.5m on the horizontal ground, and the resistance of the trolley was ▲ n. When the thrust was removed, the trolley could still advance 0.5m. This was because the trolley had ▲. When the car goes to 15.5 meters.
Answer: 20.50 inertia 750
25.(20 10, Taizhou, 6 points) Use the pulley block shown in Figure 6 to lift heavy objects. It is known that the weight of the object is 200N, and people can pull down the rope with the pulling force of 125N, which can make the object rise 2 m at a uniform speed in 5 s;
(1) tension and the work done by the power of tension;
(2) Mechanical efficiency of pulley block.
4.(20 10, Yantai, 2 points) The roller coaster is a very thrilling entertainment and leisure activity. The roller coaster sometimes rises from the lowest end of the track to the highest end, and sometimes flies down from the highest end (Figure 3). Regardless of energy loss, the following statement is correct.
A. the mechanical energy of point a is less than that of point B.
Point b.d has the largest kinetic energy, point b has the largest potential energy and point c has the largest mechanical energy.
In the process of C from A to B, kinetic energy decreases, potential energy increases, and mechanical energy remains unchanged.
In the process of D from B to C, kinetic energy increases, potential energy decreases and mechanical energy increases.
30.(20 10, Yantai, 10) With the development of society and the improvement of people's living standards, people's housing conditions have also been greatly improved. Xiaoming's family recently bought a new house. In order to help his father transport the decoration materials weighing 600N to the 6-meter-high building, Xiaoming used the pulley block he had learned in physics class to design the material handling scheme as shown in Figure 20 A.