"Mechanical Energy and Its Transformation" Work and Mechanical Energy PPT Download

"Mechanical Energy and Its Transformation" Work and Mechanical Energy PPT Download

Part One Content: Basic Knowledge Key Points

Knowledge point 1 Mechanical energy and its transformation

1. Xiao Ming throws an iron ball from the second floor to the ground. As the iron ball falls, the potential energy of gravity is converted into kinetic energy.

2. Among the following phenomena, the mechanical energy does not change (A)

A. The ball falls freely from a high place (air resistance is not considered)

B. A skydiver falls from the sky at a constant speed after parachuting

C. A child slides down the slide at a constant speed

D. An object accelerates under a horizontal pull on a smooth horizontal surface

3. On February 2, 2018, my country's first electromagnetic monitoring test satellite "Zhangheng-1" was launched from the "Long March 2D" carrier rocket and successfully entered orbit. It is the first space-based platform of my country's seismic stereoscopic observation system. . As shown in the figure, the correct analysis of energy conversion during the accelerated ascent of the rocket and "Zhang Heng-1" is (A)

A. The mechanical energy of "Zhang Heng No. 1" increases

B. The gravitational potential energy of "Zhang Heng 1" is converted into kinetic energy

C. The kinetic energy of "Zhang Heng 1" is converted into gravitational potential energy

D. The gravitational potential energy of the rocket and "Zhang Heng-1" continues to increase, and the kinetic energy remains unchanged.

4. Assume that the handball is thrown in the air and is flying. Its kinetic energy is 20 J and its potential energy is 9 J. Then the mechanical energy of the handball is (D)

A.11 J B.9 J C.20 J D.29 J

Knowledge point 2: Utilization of water energy and wind energy

5. The two Tang poems "The Yellow River is far up among the white clouds" and "The endless Yangtze River is rolling in" vividly and vividly reflect that the Yangtze and Yellow Rivers contain a large amount of mechanical energy. The purpose of building a barrage is to raise the water level upstream. When water flows out of the discharge hole of the barrage, the gravitational potential energy of the water is converted into kinetic energy. Build "windmill fields" in areas rich in wind resources to generate electricity. When the wind blows the windmill, the mechanical energy of the wind is converted into kinetic energy of the windmill blades.

6. my country will use Chang'e 4 to carry a "lunar micro-ecosystem" to grow potatoes on the moon, enabling humans to conduct biological experiments on the lunar surface for the first time. If Chang'e 4 achieves a soft landing, the lunar exploration spacecraft will slowly land on the lunar surface. In the process, the mechanical energy of the lunar exploration spacecraft becomes smaller (choose "increase", "unchange" or "get smaller").

7. As shown in the figure is a schematic diagram of the bungee jumping process, in which point A is the fixed point of the upper end of the elastic rope, point B is the position of the lower end of the elastic rope when it naturally droops when there is no one, and point C is the natural position of the lower end of the elastic rope when there is someone. The position when sagging and resting, point D is the lowest point that a person can reach during bungee jumping, then the position with the maximum speed during bungee jumping is C (optional "A", "B", "C" or "D"), from B to The energy conversion in the process of C is that gravitational potential energy is converted into kinetic energy and elastic potential energy (excluding air resistance).

Mechanical energy and its transformation PPT, part 2: improvement of comprehensive capabilities

8. As shown in the figure, a metal ball with a mass of 80 g slides freely from point a on the guide rail, passes through points b and c in sequence, and stops exactly when it reaches point d. In the process from a to b, the force of gravity The work done is 0.4 J. During the entire movement, the mechanical energy consumed by the ball to overcome the friction of the guide rail is 0.24 J (g is 10 N/kg).

9. As shown in the figure, Xiao Ming slid down two smooth slides from the same height to the bottom. In the process (C)

A. Mechanical energy is not conserved

B. The work done by gravity is not equal

C. The amount of change in gravitational potential energy is the same

D. The kinetic energy when reaching the bottom is not equal

10. The picture shows a roller coaster in an amusement park. Which of the following statements is correct (D)

A. Mechanical energy is conserved during the entire process of roller coaster movement.

B. The kinetic energy of the roller coaster is converted into gravitational potential energy during the descent.

C. When a roller coaster rushes uphill, both kinetic energy and gravitational potential energy increase.

D. The kinetic energy of the roller coaster is maximum when it reaches its lowest point.

11. The athlete stands on the ground and throws the table tennis ball vertically. After the ball hits the ground, it will bounce to a position higher than the original throw. Which of the following statements is correct (B)

A. The ball has the greatest kinetic energy when it starts to fall.

B. The ball still has kinetic energy when it bounces to the original throwing position.

C. Gravitational potential energy is converted into kinetic energy during the rising process of the ball after leaving the ground.

D. The ball’s mechanical energy increases throughout its motion.

12. As shown in the figure, let the same small ball be thrown in three different directions at the same height and at the same speed. Let the speed of the small ball when it first hits the ground be v1, v2, and v3 respectively. If the air is not taken into account, resistance, then the correct relationship between their speeds is (A)

A.v1=v2=v3 B.v1

C.v1>v2>v3 D. Unable to compare their speeds

Mechanical energy and its transformation PPT, the third part: Expanding exploration and breakthroughs

16. The gravitational potential energy of an object is related to the gravity it experiences and the height to which it is lifted. It is represented by Ep, and the relationship is Ep=Gh=mgh. As shown in the figure, the smooth arc track AB is connected to the rough plane BC. There is an existing block that starts from rest and slides down from point A, enters the horizontal plane through point B, and finally rests at point C. If the resistance on the horizontal plane is f , all the work done by gravity from point A to point C is used to overcome the resistance and do work. Please prove that the length of BC is sBC=mgh/f.

Prove: When a block slides from point A to point B on a smooth arc orbit from rest, mechanical energy is conserved, that is, kinetic energy W=Ep=Gh=mgh

All the work done by gravity from point A to point C is used to overcome resistance and work. According to W=fs, the length of BC is sBC=W/f=mgh/f

Keywords: Free download of PPT courseware for the second volume of eighth-grade physics published by People's Education Press, PPT download of mechanical energy and its transformation, PPT download of work and mechanical energy, .PPT format;

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