As shown in the figure, the displacement of a particle changes with time. The image is a parabola, and the equation is x = - 5T2 + 40t [ ] A. The maximum displacement is 80 M B. The initial velocity of the particle is 20 m / s C. The acceleration of the particle is 5 m / S2 D. When t = 4 S, the velocity of the particle is zero This is the original question If you want to ask option a, the slope becomes larger in 4-8 seconds. Is the object accelerating in the opposite direction? How is the uniform deceleration

As shown in the figure, the displacement of a particle changes with time. The image is a parabola, and the equation is x = - 5T2 + 40t [ ] A. The maximum displacement is 80 M B. The initial velocity of the particle is 20 m / s C. The acceleration of the particle is 5 m / S2 D. When t = 4 S, the velocity of the particle is zero This is the original question If you want to ask option a, the slope becomes larger in 4-8 seconds. Is the object accelerating in the opposite direction? How is the uniform deceleration

In fact, it can be seen from the image that the particle is moving at a constant deceleration with a certain initial velocity. By deriving the original equation, we can get X "= - 10t + 40. The uniform deceleration motion with an inclination rate of - 4, an initial velocity of 16m / s and an acceleration of (- 4m / S2) is 0-4s, which is the deceleration motion in the positive direction. It is stationary in 4S, accelerating in the opposite direction in 4-8s, and returning to the origin in 8s

Senior one physics (> 1)_

The distance of particle in 3 seconds is: 5 + | - 4-5 + [- 1 - (- 4)] = 17
The displacement of the particle in 3 seconds is: 5 + (- 4-5) + [- 1 - (- 4)] = - 1-0 = - 1
The displacement of the particle in the first three seconds is equal to the displacement of the particle in three seconds
The displacement of the particle in the third second is: - 1 - (- 4) = 3

As shown in the figure, it is a displacement time image of a particle motion, and the curve is an arc
A particle does not necessarily move in a straight line
The particle B may move in a circular motion with uniform velocity
The velocity of C particle first decreases and then increases
The particle D is farthest from the starting point at T1
The image looks like a parabola with an opening down
Is the answer a or C?
Isn't speed the ratio of distance to time? The image is displacement time image.
The arc is steep first and then gentle. It's like a parabola with an opening down.
If there is no picture, enter the title on Baidu and Baidu will see the picture.
The key point is item C. Speed is the ratio of distance to time, so is it a?

The vertex of the parabola is farthest from the origin, and then returns to the origin. D wrong. Before passing the vertex, it is steep first and then slow, and the speed changes from large to small, and then from slow to steep, and from small to large. C wrong. If it is a uniform circular motion, it should be a straight line, not a curve, and the image should be an inverted V, so it should be a. generally, it should be like this. I haven't seen anything of grade 1 for nearly a year