"Application of the Law of Conservation of Mechanical Energy, Understanding and Application of Functional Relationships" Excellent Courseware PPT on the Law of Conservation of Mechanical Energy

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"Application of the Law of Conservation of Mechanical Energy, Understanding and Application of Functional Relationships" Excellent Courseware PPT on the Law of Conservation of Mechanical Energy

Part One: Learning Objectives

1. Be able to flexibly apply the three expression forms of the law of conservation of mechanical energy.

2. Be able to analyze the mechanical energy conservation problem of a system composed of multiple objects.

3. Know several common functional relationships and know that work is a measure of energy transformation.

Understanding and applying the application-function relationship of the law of conservation of mechanical energy PPT, Part 2 content: 01 Exploring key points to improve literacy

1. Mechanical energy conservation problem in a system composed of multiple objects

1. For a system composed of multiple objects, mechanical energy is generally not conserved as far as a single object is concerned, but mechanical energy is often conserved as far as the system is concerned.

2. Related objects: Pay attention to find the speed relationship and displacement relationship between objects connected by ropes or rods.

3. Selection skills for the expression of the law of conservation of mechanical energy

(1) When the research object is a single object, priority can be given to applying the expression Ek1+Ep1=Ek2+Ep2 or ΔEk=-ΔEp to solve the problem.

(2) When the research object is a system composed of two objects:

① If the gravitational potential energy of two objects is decreasing (or increasing) and the kinetic energy is increasing (or decreasing), priority can be given to applying the expression ΔEk = -ΔEp to solve the problem.

② If the mechanical energy of object A increases and the mechanical energy of object B decreases, priority can be given to using the expression ΔEA = -ΔEB to solve the problem.

Summary of rules

The research object of the law of conservation of mechanical energy is a system composed of several interacting objects. The following three situations often occur:

(1) Two objects in the system are in direct contact or connected through springs. For this type of connecting body problem, attention should be paid to the conversion relationship between different energy forms between each object.

(2) Two objects in the system are connected by a light rope. If there is no problem such as friction with the outside world, only mechanical energy is transferred between the two objects, and the mechanical energy of the system composed of the two objects is conserved. The key to solving such problems is The speed of the two objects in the direction of the rope is equal.

(3) Two objects in the system are connected by a light rod. When the two objects connected by the light rod rotate around a fixed axis, the angular speeds of the two objects are equal.

2. Mechanical energy conservation problem of chain objects

The key to solving the problem of mechanical energy conservation of chain objects is to analyze the position of the center of gravity, and then determine the change in the object's gravitational potential energy. When solving the problem, we need to pay attention to two issues: one is the selection of the zero potential energy surface; the other is the change in the position of the center of gravity of each section of the chain and Changes in gravitational potential energy.

Example 2 As shown in Figure 2, a smooth and homogeneous iron chain with a total length of L spans a smooth and lightweight small pulley. At the beginning, the lower ends A and B are flush. When there is a slight disturbance, one end of the chain falls. When the chain What is the speed of the chain the moment it comes off the pulley?

3. Use the law of conservation of mechanical energy to analyze multi-process problems

Example 3 (Mid-term of the first semester of Qidong Middle School, 2019) As shown in Figure 3, the smooth tubular track ABC consists of a straight track AB and an arc-shaped track BC. The two are tangent at B and connected smoothly. O is the center of the circle, O, A On the same horizontal line, OC is vertical, a small ball of mass m with a diameter slightly smaller than the diameter of the circular pipe is connected to a block of mass M with a thin line passing through the pipe. The block is high enough from the ground. Place the ball It is released from the stationary point A. When the ball moves to B, the thin line breaks and the ball continues to move. It is known that the radius of the arc orbit is R = m, the corresponding central angle is 53°, sin 53° = 0.8, cos 53°=0.6, g=10 m/s2.

(1) If M=5m, find the speed of the ball when it moves to B;

(2) If M = 5m, find the horizontal displacement to point C when the ball drops to a height h = m after being thrown from point C;

(3) When M and m satisfy what relationship, the ball can move to point C?

Summary of rules

The law of conservation of mechanical energy is often combined with other knowledge to formulate comprehensive propositions, which are generally multi-process problems and are more difficult. When answering such questions, you must pay attention to the conditions for the conservation of mechanical energy, analyze in which process mechanical energy is conserved, and then solve it by formula. Blind application of the law of conservation of mechanical energy.

4. Understanding and Application of Functional Relationships

The relationship between work and energy: Work is a measure of energy transformation. The work done by a certain force is often related to a specific form of energy transformation. How much work is done, how much energy is transformed. The specific functional relationship is as follows:

Example 4 As shown in Figure 4, there is an arc orbit with a radius R in the vertical plane. The radius OA is horizontal and the radius OB is vertical. A small ball with a mass m starts from rest and starts to fall freely from point P directly above A. When the ball reaches the highest point B along the track, there is no pressure on the track. It is known that AP=2R and the acceleration of gravity is g, then the ball moves from P to B

A. Work done by gravity 2mgR

B. Mechanical energy reduces mgR

C. The work done by the combined external force mgR

D. Work done by overcoming friction 1/2 mgR

Example 5 (Multiple choice) As shown in Figure 5, the wooden block is stationary on a smooth horizontal table. When a bullet (can be regarded as a particle) is horizontally injected into the wooden block at a depth of d, the bullet and the wooden block are relatively stationary. When the bullet is incident During the process, the distance the wooden block moves along the table is x, and the average resistance of the wooden block to the bullet is Ff. Then in this process, the following statement is correct:

A. The mechanical energy increment of the wood block is Ffx

B. The mechanical energy reduction of the bullet is Ff(x+d)

C. The mechanical energy reduction of the system is Ffd

D. The mechanical energy reduction of the system is Ff(x+d)

Understanding and application of the application-function relationship of the law of conservation of mechanical energy PPT, part three content: 02 in-class drills, point-by-point implementation

1. (Functional relationship) (Multiple choices) (End of the first semester of 2018·Baishui Middle School) As shown in Figure 6, an object with mass m (can be regarded as a particle) rushes from point A at a certain speed with an inclination angle of 30° is a fixed inclined plane, the acceleration of its movement is 3/4g, and the maximum height of this object rising on the inclined plane is h, then during this process the object

A. Gravitational potential energy increased by 3/4 mgh

B. Overcome friction and do 1/4 mgh of work

C. Kinetic energy lost 3/2mgh

D. Mechanical energy is lost by 1/2mgh

2. (Chain type mechanical energy conservation problem) (2018·Shude Middle School Final) As shown in Figure 7, a soft homogeneous chain with a length of L initially rests on a smooth trapezoidal platform. The length of the chain on the inclined surface is x0. It is known that the acceleration due to gravity is g,

Lx0), the speed of the chain is ____________________. (expressed by x0, x, L, g, α)

3. (Calculation of the conservation of mechanical energy of the system) (2018·Zhengding Middle School Final Examination) As shown in Figure 8, small balls A and B of mass m are fixed at both ends of a hard straight rod regardless of mass. They can revolve around the smooth axis O Rotate freely in the vertical plane. It is known that OA=2OB=2l, release the rod from the horizontal position from rest. (The acceleration of gravity is g)

(1) When the rod rotates to the vertical position, what are the speeds of balls A and B?

(2) How much work does the rod do on ball A when the rod rotates to the vertical position?

(3) At the moment when the rod just turns to the vertical position, what is the force exerted by the rod on ball B? Is it push or pull?

Keywords: PPT courseware for high school physics compulsory course 2 from the People's Education Press is free to download, understanding and application of the application-function relationship of the law of conservation of mechanical energy PPT download, law of conservation of mechanical energy PPT download, .PPT format;

For more information about the PPT courseware "Law of Conservation of Mechanical Energy, Understanding and Application of Functional Relationships in the Application of the Law of Conservation of Mechanical Energy", please click on the Law of Conservation of Mechanical Energy PPT, Understanding and Application of Functional Relationships in the Application of the Law of Conservation of Mechanical Energy PPT tag.

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Update Time: 2024-10-10

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