Junior High School Physics Speed Problems An object moves from a standstill, next .

Known: total distance = 6900 meters.

Find: The average speed of the whole journey = ?

Solution: Total time = 150 seconds + 100 seconds + 50 seconds = 300 seconds.

Average speed = total distance Total time = 6900 meters 300 seconds = 23 meters per second.

A: The average velocity of the object is 23 meters per second more than the entire journey.

Solution: t=t1+t2+t3=150 seconds + 100 seconds + 50 seconds = 300 seconds.

s = 6900 meters.

v=s t=6900m 300s=23 meters per second.

A total of 6900 meters, 150 seconds after deceleration, indicating that the movement is 150 seconds, and the constant speed is 100 seconds, that is, 150 + 100 stops after 50 seconds, that is, a total of 150 + 100 + 50 = 300 seconds, and then the distance is divided by time.

Because average speed = distance time, the average speed is.

6900 (150+100+50)=23 m/s.

Look at the question The time spent in the whole process.

150 + 100 + 50 = 300 seconds.

The distance covered is as follows:

6900 meters.

So the average speed of the whole journey is:

6900 300 = 23 meters per second.

Average speed = distance time.

The whole process takes t=150+100+50=300 seconds.

Average speed = 6900 300 = 23 meters per second.

Average speed = distance Time = 6900 (150 + 100 + 50) = 23 meters per second.

Average speed v = total distance travel.

6900 (150+100+50)=23 m/s.

C. Question analysis: According to the image of acceleration with time, the <> is a uniform acceleration linear motion with a <> velocity

The velocity is in the positive direction, and the answer d is false. The speed at the end of the first second <>

The acceleration becomes negative, while the velocity is in the positive direction, so it is a deceleration, <> when the velocity decreases to 0 at the end of the second second, the answer B is false. <>

The acceleration is in the positive direction, the initial velocity is 0, and the object is in a uniform linear motion in the positive direction<> that is, the previous motion is repeated from the second second, and the image is as follows: C answer C is true and A is false.

Answer: A. When the acceleration is constant, the DU object may move in a straight line, or it may move in a curved line, such as a flat throwing motion, so a is wrong

b. For an object with zero initial velocity, the object does not necessarily move in a straight line, so B is wrong C. The direction of velocity and acceleration are not in the same straight line, and the object must move in a curve, so C is correct

d. When the direction of acceleration is perpendicular to the direction of initial velocity, it is not necessary to do circular motion, for example, the direction of initial velocity of flat throwing motion is perpendicular to the direction of acceleration, so D is wrong

Therefore, c

1.Wrong.

2.Inertia is an intrinsic property of an object, and all objects have inertia. The only measure of the magnitude of inertia is the mass of the object, and the greater the mass of the object, the greater the inertia.

Inertia has nothing to do with whether or not an object is forced, how it is forced, whether or not the object is moving, how it moves, and whether the object is located in a geographical location.

3.The essence of inertia is different from the law of inertia (Newton's first law).

1) Inertia is a property of an object that keeps its original state of motion unchanged, regardless of whether the object is subjected to force and the magnitude of the force. (2) Newton's first law of inertia reflects the motion of an object under certain conditions (when there is no external force [or when it is balanced]).

1. Inertia, inertia, is a characteristic that is embodied when changing the state of motion or rest;

2. It is more obvious in the process of changing from rest to motion, or from motion to rest;

3. Change the state of motion or change the state of rest, and the inertia is not limited to stationary or uniform linear motion;

4. In fact, the English moment of inertia is moment of inertia, which shows that in rotation, inertia.

The nature is reflected in the moment of inertia, and the radius of rotation in engineering comes into being.

As long as an object has mass, it has inertia and has nothing to do with the state of motion.

(1) Let the velocity of the object at the beginning of this 1s be v

then s=vt+at 2=15m

Substituting a=2m s and t=1s gives v=14m s(2) and sets the time of the motion t0

then v=0+at0=14m s

Substituting a=2m s gives t0=7s

3) The distance that has been passed s0 = at0 2 = (2 7 2) m = 49m uniform speed linear motion problem often has to be calculated from this kind of weird place (a certain 1s on the way, the last 1s, etc.), it is best to think of the simplest way is like this solution, don't think too much, write formulas, algebras, and then just write the answer like a general equation.

1。Let the velocity at the beginning of 1s be v0 and the velocity at the end of 1s be v, then there is v 2-v0 2=2as

v=v0+at

The solution is v0 14m s

2。Let what you want be t.

at v0, solution t 7s

3。Let what you ask for be s.

v0^2=2as

Solution to 49m.

s=a/2t^2=t^2

Let t2-t1=1

then s2-s1=15

So s1=t1 2

s2=t2^2

Therefore s2-s2=t2 2-t1 2=(t2-t1)*(t2+t1)=15

t2+t1=15

t2=8, t1=7

1) The velocity of the object at the beginning of this 1s = s'(t1)=a*t1=2*7=14 (m/s)

2), how long has the object been moving before this 1s = t1 = 7s (3), how many distances the object has passed before this 1s = s1 = t1 2 = 49m

The problem is that the velocity of the nuclear engraver in the middle is vtm=v2, and at the midpoint, it is obtained by 2ax=v2 v2xm=v2xm, and vxm=2 v2. Therefore, item b is correct. As mentioned above, the correct answer to this question is B.

Inertia is an intrinsic property of all objects, whether solid, liquid, or gas, whether the object is in motion or at rest. Everything has inertia. Definition of inertia:

We call the property of an object that remains in constant motion inertia. Inertia represents how easy it is for an object to change its state of motion. The magnitude of inertia is only related to the mass of the object.

It is relatively difficult to change the motion state of an object with a large mass, that is, it has a large inertia; The motion state of an object with a small mass is relatively easy to change, that is, the inertia is small. When you kick the ball, the ball starts moving, and because the ball itself is habitually piercing and flat, it will keep rolling until it is stopped by an external force.

Any object has inertia at all times, and it has to maintain its original state of motion.

Newton's first law shows that any object that is not subject to force remains at rest and moves in a straight line at a uniform speed. For example, if the car brakes from the movement and suddenly stops, the upper body of the person inside will lean forward because of inertia, because the lower body of the person has started to move with the car and the upper body of the person should maintain the original state of motion, so the body will lean forward...

Even if he is still, he will continue to stay still, and he wants to stop after exercising, but he will continue to move before he stops slowly, and braking and running can be fully reflected.

Both motion and rest are relative to the referent.

Motion is the form of existence and intrinsic property of matter. It includes all the changes and processes in the universe. Dialectical materialism holds that the world is material, and matter is in eternal motion.

Matter and motion are inseparable, and there is no matter in the world that does not move, and there is no movement that leaves matter.

Dialectical materialism holds that motion is an intrinsic property and mode of existence of matter, which is absolute and unconditional, but does not deny stillness. It points out that rest is a special case of motion when it is examined in a certain relationship, which is relative and conditional.

Although everything is in motion all the time, a specific thing may not have a certain form of motion on a certain occasion. To the extent that it does not have this particular form of motion, it is stationary. For example, a building on the ground is stationary in the sense that it is not mechanically moving to the ground.

But this stillness is only from a certain"Frame of reference"It seems that this is the case, from something else"Frame of reference"It seems to be in motion, such as buildings orbiting the sun with the ground, moving in the Milky Way with the solar system, and so on.

Everything is in motion all the time, but not all of them change qualitatively. When a thing has not yet undergone a qualitative change, the thing is still itself, and in this sense it is static. For example, when the number of protons in the nucleus does not change, it is still the atom of a certain chemical element and not the atom of another chemical element; While the economic base and superstructure of capitalist society still exists, it remains capitalist and not otherwise.

But in the absence of a change in the chemical properties of atoms, in the absence of a change in the nature of capitalist society, their internal movements are still in motion, and in the final analysis, they are going to cause a qualitative change in them. Therefore, stillness is conditional, temporary, relative, and only a manifestation of motion, while motion itself is unconditional, eternal, and absolute.

It is not a purely negative and conservative factor, but a necessary condition for the existence and development of things.

It is precisely because things have a relatively static aspect that they can become things with definite properties and definite forms of motion and stillness, and can exist and develop, and be recognized and used by people. Modern science has shown that even microscopic particles with extremely short lifespans have a relatively stationary side at the moment of their existence, and have definite properties that can be observed and described.

It is precisely because things have a relatively static aspect that the motion of things becomes something that can be measured and calculated. For example, to calculate the displacement of an object, it is necessary to select a certain frame of reference as the framework at rest; This choice is possible because relative stillness exists objectively.

It is precisely because things have a relatively static aspect that it is possible to grow new factors within things, and to prepare the conditions for the development of things into a higher form. For example, all social forms have a relatively stable or relatively static aspect, so that the productive forces can develop internally, and finally promote the transformation of a social form into a higher social form.

Judging whether an object is at rest or in motion is relative to the reference object, and it is necessary to explain the state of motion of another object according to the state of the reference object, whether it is stationary or in motion.

Motion and rest are divided into two concepts, one is absolute and the other is relative. Middle school physics is about the concept of relativity. For example, bus stop signs and buses, the bus stops at the stop sign and does not move, we say that the car is stationary.

The car is moving, and we say the car is moving. For example, when the foot is not kicked out, the football is placed on the turf, it is stationary, and after being kicked out, the football is moving relative to the turf. Generally, junior high school students need to master an average speed, which is v=s t (distance divided by time).

Motion and rest are relative, depending on the reference you choose.

It is to see if one object is moving relative to another.