Physics Problems The following movements are not possible

You are drilling the tip of the horns, acceleration = 0 means no acceleration, so there is no need to talk about the same acceleration. Or d.

a.If the direction of acceleration is opposite to the direction of motion, it is true;

b.The direction of acceleration is the same as the direction of motion, and as long as there is acceleration, the velocity increases. Establish.

c.The moment when the object is just beginning to move, it is established.

d.If there is acceleration, there will be a change in velocity, so d is wrong.

a. As long as the acceleration is in the opposite direction of velocity, the object decelerates.

b. If the object is thrown upward, the velocity direction changes to the highest point, and the acceleration direction is unchanged.

c. If the object suspended under a spring is vibrating, when it reaches the highest point or the lowest point, it is "when the acceleration is maximum, the smaller the velocity."

d. Acceleration, which is the rate of change of velocity. If the acceleration is zero, the velocity does not change, and the change in velocity must be zero. Pick D

You can only think that the questioner has defaulted to the acceleration Velocity unchanged = acceleration Velocity is not equal to zero.

It's the question of the person who made the question, not your question.

If the acceleration is zero, there is no acceleration and this assumption is not in the question, so don't have that assumption.

I don't think the question is rigorous, and the uniform speed straight line of option d is also It's okay to say that the default acceleration velocity of the question is not zero.

In the following motions, can stillness be regarded as a kind of motion?

The following selections are pure muffled neck masks that do not belong to the three types of physics to do the age of exercise ().

a.Accelerate your movements.

b.Constant motion.

c.Uniform speed movement.

d.Unsure of movement.

Correct Answer: a

The answer is c. The details are as follows:

a.Acceleration gradually decreases, while velocity gradually increases: it can happen. When the direction of the Gasilis velocity coincides with the direction of the initial velocity, the acceleration gradually decreases, while the velocity still increases gradually, but the amount of increase per second decreases.

b.The direction of acceleration does not change, while the direction of velocity changes: it can happen. For example, in the direction of acceleration (gravitational acceleration), the direction of acceleration (gravitational acceleration) remains the same, but the direction of the velocity is constantly changing.

c.Acceleration does not change, velocity does not change: it cannot happen. There is acceleration, and the velocity of the object must change, because acceleration is a physical quantity that describes how fast or slow the velocity of an object changes.

d.Acceleration increases and decreases in velocity: it is possible. When the direction of acceleration is opposite to the direction of initial velocity, the acceleration gradually increases, but the quick-freezing gradually decreases.

a possibly, for example, acceleration and velocity in the same direction, acceleration decreases, and velocity increases.

b is too likely, for example, there is an angle between the acceleration vector and the velocity vector, as long as the angle is not 0 degrees and 180 degrees;

If the satellite runs in a circular orbit, the acceleration of the height and width of the satellite remains the same, and the direction changes, and the velocity of the satellite remains the same, but the direction changes!

dIf the satellite is in elliptical orbit, the acceleration and speed of the satellite will change, the speed of the satellite is the smallest when the acceleration is maximum (apogee), and the speed is the largest (perigee) when the acceleration is smallest! Qi matching.

so, the answer is c, the direction of velocity has changed;

In this way, find a real-life example for the problem, and verify the same, OK, (note that velocity and acceleration are vectors!) ）

Answer b Acceleration is decreasing, as long as the direction of acceleration is the same as the direction of velocity, the velocity increases, a is possible As long as there is acceleration, the speed has to change, b is not possible In the process of starting the car from starting to reaching the maximum speed, the acceleration gradually decreases, and the speed is gradually increasing, when the velocity is zero, the acceleration is the largest fiber base, and when the velocity reaches the maximum, the acceleration is zero, c is possible When the object is decelerating, when the velocity decreases to zero, it begins to accelerate in the opposite direction, d is possible

a. The speed of the change of velocity is the magnitude of the acceleration, so A is wrong B, the direction of change of velocity is the direction of acceleration, and B is wrong.

C. The reason for the analysis of the same as A, and C is wrong.

d. There is no direct relationship between the magnitude of acceleration and the magnitude of velocity, and the magnitude of acceleration is related to the speed of change, so d is right.

The answer is: d.

For example, the process of starting a car is.

Select: d. The speed increases all the time when the direction is the same.

Pick the fourth. The first one: it went forward before, now it goes backwards, and now it accelerates, so you can increase the speed and decrease the displacement.

The second one: before walking forward with a certain acceleration, and then changing the direction of acceleration to the back, it becomes a deceleration.

Thirdly, the object is at rest, subjected to a large force, and the acceleration is great at the very beginning of the force, but the velocity is zero.

The fourth one is probably impossible. It says that the acceleration decreases (decreasing generally means a decrease in value, and it also says that the acceleration and the velocity are in the same direction), then there is still an acceleration and it will accelerate in the original direction (even if the acceleration decreases to zero, according to Newton's first law, he should not become velocity, and it is impossible to decrease the velocity).

d……said that the only one would, but someone replied ......

The answer is A

The constant state of motion means that the velocity and direction of the object are both dissipated, so only a is correct

Speed is the lead shirt sign of the state of motion of an object

The first step is to calculate the time it takes for the wooden box to move when the ball falls.

According to the inscription, the wooden box is subjected to a net force before the small metal block falls.

f=9n-f=9n- mg=

According to s=12at2=12(fm)t2

Yields: 1=(1 2)*(1 2)t 2

Because the wooden box is 1m long, it is s=1, and the upper surface of the wooden box is smooth, so only the wooden box does the acceleration movement, so m=2kg).

The solution is t=2 seconds<3 seconds, so it is in line with the topic, and after the small metal block falls, the wooden box will continue to be subjected to constant force for 1 second.

In the second part, calculate the speed of the wooden box when the metal block falls.

v=at=(1/2)*2=1m/s

The third step is to calculate the distance that the wooden box moves after the small metal block falls, that is, the distance between the small metal block and the left edge of the wooden box after it is stationary.

In 1 second when the constant force continues, the net force experienced by the wooden box is 9-(, then the acceleration is 4 2 = 2m s 2

The travel distance is vt+(1 2)at 2=1*1+(1 2)*2*1=3m

And the final velocity is v+at=1+2=3m s

After the constant force is removed, the net force of the wooden box is only frictional force-(

Then the acceleration is -5 2=

The travel distance is vt+(1 2)at 2=3*t+(1 2)*(

The movement time is 3 (seconds (because it is decelerated from 3m s to stop, and substituted by the above equation).

s2 = the distance that the wooden box moves after the small metal block falls, that is, the distance between the small metal block and the left edge of the wooden box after it is stationary = 3+