Is it still a system when an object in a connected body moves relative to each other? 100

When the object in the connecting body is relatively variable speed movement, it is still not a system, it is artificially identified (it can be identified as a system, and it can also be identified as divided into several systems), and it is relatively simple to solve depending on which division is relatively simple.

- Velocity (vector, magnitude and direction) change (or magnitude or direction) (i.e. a≠0) is called variable speed motion;

Motion with constant velocity (i.e., a=0) and constant direction is called uniform motion;

Variable speed motion is divided into uniform variable speed motion (constant acceleration) and variable acceleration motion (acceleration change).

Therefore, the variable acceleration motion is not for the variable deceleration motion, but for the relatively uniform variable speed motion.

Uniform speed movement.

Motion with constant acceleration (must be of the same magnitude and direction).

Uniform speed motion can be either linear motion (uniform speed linear motion) or curved motion (e.g., flat throwing motion).

Chinese name. Variable speed movement.

Field. Physics.

Conception. Changes in the speed of movement.

Quality. Noun.

Fast. Navigation.

Variable acceleration movement.

Uniform variable speed linear motion.

Conception. 1. Definition of linear motion with uniform variable speed: the motion along a straight line with constant acceleration is called linear motion with uniform variable speed. When the acceleration and velocity are in the same direction, the object moves in a uniform linear motion, and when the acceleration and velocity are reversed, the object moves in a uniform and decelerated linear motion.

2. The characteristics of uniform variable speed linear motion: the magnitude and direction of the acceleration of uniform variable speed linear motion do not change with time.

3. Uniform speed linear motion is also an ideal motion process.

4. When the acceleration and speed are in the same direction, the uniform deceleration moves in a straight line.

Formula. 1 Speed formula: v2=v1+at

2 Displacement time formula: x=(v1+v2)*t 2=v1*t+1 2at 2

3 Displacement velocity formula: 2ax=v2 2-v1 2

It's the right answer.

Because of this, when the state of motion changes, either the magnitude of the velocity changes, or the direction changes, or both, otherwise it is a straight line with a uniform velocity or a state at rest. The most important thing is that you have to grasp the concept of speed, speed is a vector, if the speed is constant, it must be the size and direction of the speed! Otherwise, it is variable speed motion, which is consistent with the vector concepts of displacement, force, electric field strength, etc.

The concept of vector is clear in our physics textbooks, so if the state of motion of an object changes, the object must be in variable motion.

a. According to the condition of conservation of mechanical energy, only gravity or elastic force does the work If it is only gravity that changes the speed of the object, it means that only gravity does the work, then the mechanical energy of the object remains unchanged so a is correct

b, c, velocity is a vector, if the speed of the object is not changed by gravity, elastic force, but friction, if only the direction of the speed is changed, the kinetic energy of the object does not change, then the mechanical energy of the object is still unchanged For example: the wooden block is placed on the horizontal disc and rotates with the disc at a uniform speed, the static friction force provides centripetal force, the direction of velocity has been changing, but the speed is the same, so the mechanical energy is unchanged Therefore, b and c are wrong

d. The kinetic energy increases, if the gravitational potential energy decreases, and the amount of gravitational potential energy decreases greater than the amount of kinetic energy increases, then the mechanical energy decreases, so d is correct

Hence the choice: AD

a. According to the condition of conservation of mechanical energy, only gravity or elastic force does work, mechanical energy is conserved, if gravity only changes the state of motion of the object, it means that only gravity does the work, then the mechanical energy of the object remains unchanged so a is correct

b, c: velocity is a vector, if only the direction of the velocity is changed, the kinetic energy of the object does not change, then the mechanical energy of the object is still unchanged For example: the wooden block is placed on the horizontal disc and rotates with the disc at a uniform speed, the static friction force provides centripetal force, the direction of velocity has been changing, but the velocity magnitude is unchanged, so the mechanical energy is unchanged Therefore, BC is not correct

d. The increase in kinetic energy does not mean that the mechanical energy must increase, but it may also decrease, because the mechanical energy is the sum of kinetic energy and potential energy, so d is correct

Hence the choice: AD

t=x v So the first 20 meters take 4s

t total tease Sakura Xiang = 4+

x total = v flat mountain fight t =

End of x = x total -x first two segments =

So the end of the ode silver v = the end of x and the end of t =

a. According to the condition of conservation of mechanical energy, only gravity or elastic force does work, mechanical energy is conserved, if gravity only changes the state of motion of the object, it means that only gravity does the work, then the mechanical energy of the object remains unchanged so a is correct

b, c: velocity is a vector, if the speed only changes the direction of the velocity, the kinetic energy of the object does not change, then the mechanical energy of the object is still unchanged For example: the wooden block is placed on the horizontal disc and rotates at a uniform speed with the disk, the static friction force provides centripetal force, and the direction of the speed is changing, but the speed is unchanged, so the rolling sensitive mechanical energy of the machine mu is unchanged, so the bc is not correct

d. The increase in kinetic energy does not mean that the mechanical energy must increase, but it may also decrease, because the mechanical energy is the sum of kinetic energy and potential energy, so d is correct

Hence the choice: AD

a. According to the condition of conservation of mechanical energy, only gravity or elastic force does the work If it is only gravity that changes the speed of the object, it means that only gravity does the work, then the mechanical energy of the object remains unchanged so a is correct

b, c, velocity is a vector, if the speed of the object is not changed by gravity, elastic force, but friction, if only the direction of the speed is changed, the kinetic energy of the object does not change, then the mechanical energy of the object is still unchanged For example: the wooden block is placed on the horizontal disc and rotates with the disc at a uniform speed, the static friction force provides centripetal force, the direction of velocity has been changing, but the speed is the same, so the mechanical energy is unchanged Therefore, b and c are wrong

d. The kinetic energy increases, if the gravitational potential energy decreases, and the amount of gravitational potential energy decreases greater than the amount of kinetic energy increases, then the mechanical energy decreases, so d is correct

Hence the choice: AD