A detailed analysis of several high school compulsory 1 physics problems

2: a=(vt-v0) t, t is a scalar, a and v are vectors, and they are in the same direction.

3: It's the same, what to look at, physics questions generally don't use any coordinates.

4: No, because the particle should meet the difference between the measured result and the measurement, assuming that you take the person as the quality point, then we will take his center of gravity as a point (probably the position of the navel), then the measurement result is the height of the ground from the sole of the foot plus the height of the sole of the foot from the navel...

If you can jump to Mars, this height is negligible, and that's okay.

1. According to the definition, it can be judged that it is not a uniform linear motion in the whole process.

2. Still according to the definition, the direction of acceleration is the direction of the amount of velocity change, which is understood in the form of vectors, in fact, the direction of acceleration has been changing, which is only the direction that can be understood as the average acceleration for a period of time.

3. What is this said in practice? You need to specify the coordinate system!

4. No, it depends on whether the relative size of the measured data and the actual geometric length of the object affects the results. Thank you!

1.It doesn't count, because according to the judgment theorem, the acceleration changes, 2That formula is actually a vector formula, not an ordinary formula.

According to the nature, 2 vectors with the same direction are added, the direction is unchanged, and the magnitude is subtracted, (high school compulsory 2) The example is not easy to give and the pure math problem, you can imagine the change of v after the synthesis of 2 forces.

3.How can a coordinate system have units, and (on behalf of (4 m, 3 m) 4To do physics problems, you must turn them into mass points, and at half of your height, forget it in the Olympics.

1.It does not count as a uniform linear motion throughout the whole process.

t has no direction, so a and v are the same.

3.Either way. 4.Yes, because only its displacement is calculated without taking into account its state of motion.

1.Not counted. , t has no direction, then a and v are in the same direction.

3.I think it's all right.

4.Yes,

Biology exercises and questions.

a force is the cause of changing the state of motion of the object, for this problem, since f1 f2 is always true, the resultant force always has an acceleration to the right of the object, so its velocity always increases until it is maximum.

f1>f2 so f1-f2>0 ma = f1-f2>0 so a 0, the velocity gradually increases. But f1 is decreasing, so a is also decreasing, and when a is 0, the velocity increases to its maximum.

The acceleration has been to the right, and I know that it is reduced to zero, so I have been accelerating to the maximum!!

Because f1 is greater than f2, the object moves to the right, and when f1 is equal to f2, the object is not affected by the force and moves at a uniform speed, so the velocity reaches its maximum.

- - Let's put it this way: The object starts moving to the right because f-junction=f1-f2 is to the right.

After that, f1 gradually decreases, but it is still greater than f2, so the direction of velocity is still to the right, but the resultant force decreases, so the acceleration also decreases, and finally f1 = f2 when the acceleration decreases to zero, and the velocity is at its maximum.

a。Explanation: The acceleration is positive in 1 second, and the direction of velocity is unchanged; The direction is negative for 2 seconds, and the deceleration is until it reaches 0, but the direction of the velocity does not change; Clause.

The change in the direction of acceleration within three or four seconds is positive, that is, acceleration, but the direction of velocity remains unchanged; Decelerates in seconds, but still moves in one direction.

B is false, because the velocity is reduced to 0 in the second second, and the acceleration is still negative in the third second, moving in the opposite direction.

c and d represent velocity and displacement, and since positive and negative represent direction, it does not move in a single direction.

Correct Answer: Rectilinear motion of ABCD oil round trip.

1 Because the object is at rest and only receives two forces, one gravitational and the other is the pulling force of the rope, these two forces constitute a balance of two forces, so it must be collinear and the center of gravity will be below the rope.

2 In this question, you can think of a spring as a spring scale, the upper end of the spring is the hook of the spring scale, and the reading of the spring scale is equal to the tension of the hook end (this is because the spring studied in high school is lightweight). In this problem, although the lower ends of the four springs are different, the upper ends are all pulled by the same force, so the readings should be the same, and the spring scale readings are proportional to the elongation (this is because of Hooke's law), so the elongation of the four springs is the same.

The elastic force in the light spring is equal everywhere, so the elastic force in these four springs is equal to f, i.e., f=kx, and k is the same, so x is the same, i.e., l 1 = l 2 = l 3 = l 4, independent of the other forces acting on the block and the state of motion of the block.

If the total distance is s, then the original planned time is t=s 30

The actual situation is: the first half of his journey takes t1=(s 2) 15=s 30, which shows that t1=t, that is, he runs out of time in the first half of the journey, and the time of the second half of the journey can only be zero, which means that his speed must reach infinity.

If the two displacements are in the same direction, the displacement reaches the maximum value.

If the two displacements are in opposite directions, the displacement reaches a minimum.

If the two displacements are at a certain angle, the resultant displacement is between -6m and 15m according to the triangle rule, so the total displacement is greater than or equal to -6m and less than or equal to 15m

This is the first three seconds of the displacement is positive, if the last three seconds are positive, it is greater than or equal to -15m and less than or equal to 6m).

You should mean a uniform acceleration motion with an initial velocity of 0, and the first three seconds 1 2at squared = solution a = 1

After three seconds, 1 2at squared-1 2a(t-3) squared = solution t=5 means that the object has been in motion for 5 seconds.

Total displacement 1 2at squared =

If the direction is reversed, the total displacement is a minimum of 6 meters.

If the direction is the same, the total displacement is up to 15 meters.

So the total displacement is between 6 meters and 15 meters.

If there is no change of direction in the first three seconds, and no change of direction in the last three seconds, there are two cases (the first three seconds are specified as the positive direction):

1.The first three seconds, the last three seconds in the same direction:

2.The first three seconds, the last three seconds are in different directions:

The displacement formula for linear motion with uniform velocity is x=vt+1 2at 2 and the formula in the problem is s=10t+t

So the initial velocity v=10m s 1 2a=1 i.e. a=2m s 2, so the velocity at the end of 3 seconds v=10+2*3=16m, s displacement=10*3+3*3=39m

If the displacement of a particle moves in a linear motion with uniform variable speed, and the relationship between its displacement and time is s=10t+t (m), the velocity of the particle at the end of 3s is 16 m s, and the displacement in the 3s is 39 m

The shape of the trajectory is determined by the relationship between the force and the initial velocity or the acceleration and the initial velocity of the object, if the force and the initial velocity move in a straight line (uniform motion is done when the resultant force is zero, uniform acceleration motion is done when the force and initial velocity are in the same direction, and uniform deceleration motion is done in reverse); The force and initial velocity do not move in a straight line. Therefore, this problem first requires the direction of the resultant force and the direction of the initial velocity, and the method is: the resultant force in the x direction and the y direction is synthesized from the parallelogram rule of force to the direction of the resultant force of the object; Then according to the direction of the initial velocity of x and the direction of the initial velocity of y, the direction of the combined velocity is also calculated according to the parallelogram rule, and it can be found that they are in the same direction, so do a uniform acceleration motion, note:

The initial velocity and force in the X direction are negative, so the force and initial velocity in the X direction are also in the same direction, so the X direction is also a uniform acceleration motion, and the correct answer to this question is: B

Select d, do the uniform acceleration linear motion of v0=-4 and a=-4 in the x-direction, and the uniform acceleration linear motion of v0=6 and a=6 in the y-axis, and combine the two together to do the curvilinear motion.

The first derivative of displacement to time is velocity, x=-2t2-4t, y=3t2+6t, therefore: vx=-4t-4, vy=6t+6;

Therefore, the initial velocity: v0x=-4m s, v0y=6m s;

The first derivative of velocity to time is acceleration, so acceleration: ax=-4m s2, ay=6m s2;

The initial velocity and acceleration of the object on the x-axis are in the same direction, and they are moving in a uniform linear motion;

The initial velocity and acceleration of an object in the y-axis direction are in the same direction and are moving in a straight line with uniform acceleration;

The initial velocity and acceleration values of the sub-motion are exactly the same, so the values and directions of the combined motion are also the same.

The direction of the initial velocity of the combined motion is the same as the direction of acceleration, so the combined motion must be a uniform acceleration linear motion;

So the answer is: straight line

This formula is used to find the uniform variable speed motion: average velocity = (v1+v2) 2 = instantaneous velocity at intermediate momentsImage Method:

Draw a v-t image, from the knowledge of geometry (t1+t2) 2 when the velocity is v0=(v1+v2) 2 do the image of y=v0, you can see that the two straight lines and the x-axis enclose the same area, so....

This is specific to constant speed movement, and can be launched according to the average speed formula and instantaneous speed formula for constant speed movement.