As shown in the figure, the ball falls from a high place to a light spring placed vertically. From contacting the spring to compressing the spring to the shortest distance, the correct one in the following description is () A. The velocity of the ball decreases all the time B. the acceleration of the ball decreases all the time C. The maximum value of the acceleration of the ball must be greater than the acceleration of gravity D. the velocity of the ball is the maximum at the midpoint of the displacement in this process

As shown in the figure, the ball falls from a high place to a light spring placed vertically. From contacting the spring to compressing the spring to the shortest distance, the correct one in the following description is () A. The velocity of the ball decreases all the time B. the acceleration of the ball decreases all the time C. The maximum value of the acceleration of the ball must be greater than the acceleration of gravity D. the velocity of the ball is the maximum at the midpoint of the displacement in this process

A. B, D, from the beginning of the contact spring to the shortest process of compressing the spring, the gravity is greater than the elastic force, and the acceleration is decreased when the elastic force increases in the process of descending. When the acceleration decreases to zero, the speed reaches the maximum, and then the gravity is less than the elastic force, and the acceleration is increased when the gravity is downward, and the speed reaches the lowest point is zero So a and BD are wrong. C. when the ball moves to the lowest point, the acceleration is the maximum. If the ball falls from the original position of the spring, according to the symmetry of the motion, the acceleration at the lowest point is g, and the direction is upward. If the ball falls from a certain height, and the lowest point is lower, the acceleration is greater than g. so C is correct