"Optimization Summary of this Chapter" Research on Uniform Speed ​​Linear Motion PPT

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"Optimization Summary of this Chapter" Research on Uniform Speed ​​Linear Motion PPT

Integration and improvement

Common methods for finding uniform variable speed linear motion

Since there are many formulas in the kinematics part, and the formulas are related to each other, some of the questions in this chapter can often be solved multiple times. When solving problems, you should broaden your mind, associate and compare, and select the most convenient solution to simplify the problem-solving process. The commonly used problem-solving methods and regular characteristics in this chapter are shown in the table below:

Commonly used methods Regular characteristics

Formula method Use the basic formulas of uniform linear motion to solve problems: speed formula vt=v0+at; displacement formula s=v0t+12at2; displacement and speed relationship 2as=v2t-v20. The three formulas are all vector formulas. Pay attention to the relationship between each physical quantity when using them. direction

The average speed method definition v=st is applicable to any linear motion, while v=12 (v0+vt) is only applicable to uniformly variable linear motion. Appropriate use of the average speed formula can help improve problem-solving speed

Intermediate moment velocity method In uniform linear motion, the instantaneous speed at the intermediate moment in any time t is equal to the average speed during this period, that is, v = v. This conclusion is applicable to any uniform linear motion. Applying it to some problems can avoid the complex formulas containing t2 listed by the displacement formula in the conventional solution method, thus simplifying the problem-solving process and improving the speed of problem-solving.

[Exercise to achieve standards]

1. (Multiple choices) (2018•National College Entrance Examination Paper III) Two cars A and B are moving in the same direction on the same straight road. A is moving in a straight line with uniform acceleration, and B is moving in a straight line with uniform speed. The changes in the positions x of vehicles A and B with time t are shown in the figure. Which of the following statements is correct ()

A. At time t1, the speed of the two cars is equal.

B. From 0 to t1, the distance traveled by the two vehicles is equal.

C. From t1 to t2, the distance traveled by the two vehicles is equal.

D. At a certain time from t1 to t2, the speed of the two cars is equal

2. (Multiple choice) The s-t image of object A and the v-t image of object B are as shown, then the motion of the two objects is ()

catch up, encounter problems

1. Follow up on issues

(1) Characteristics of catch-up: two objects are in the same position at the same time.

(2) Trace the two relationships that satisfy the problem

① Time relationship: From the time the object behind catches up to the time it catches up with the object in front, the time experienced by the two objects is equal.

②Displacement relationship: s2＝s0＋s1

Among them, s0 is the distance between the two objects when chasing starts, s1 represents the displacement of the object being chased in front, and s2 represents the displacement of the object chasing behind.

(3) Critical conditions: When the speeds of two objects are equal, situations such as catching up, avoiding collision, being farthest from each other, or being closest to each other may occur. That is, the critical condition for the above four situations is v1 = v2.

2. encounter problem

Objects moving toward each other meet when the sum of the absolute values ​​of their respective displacements is equal to the initial distance between the two objects. In the collision avoidance problem, the key is to grasp the critical state. The critical state of the collision avoidance problem is still reflected in the key point of equal speed, that is, when two moving objects have the same position coordinates, the relative speed of the two is zero.

3. General methods for analyzing and pursuing problems

(1) General problem-solving ideas

(2)Problem-solving skills

① Grasp the three relationships, namely "displacement relationship", "time relationship" and "speed relationship"; use the schematic diagram well.

②Looking for implicit critical conditions, such as "just right" and "just right" are often the breakthrough points in solving problems.

③If the object being chased slows down, determine when it stops.

regular method

General ideas for solving problems of pursuit and encounter

(1) Based on the analysis of the motion process of the two objects, draw a schematic diagram of the motion of the objects.

(2) According to the motion properties of the two objects, list the displacement equations of the two objects respectively. Be careful to reflect the relationship between the motion time of the two objects in the equations.

(3) Find the correlation equation between the displacements of the two objects from the motion diagram. This is the key.

(4) Solve the simultaneous equations and conduct a simple analysis of the results.

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Update Time: 2024-07-08

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