If the elevator stops suddenly, the observer on the ground will see that the ball is in the process of continuing to rise () A. The velocity decreases gradually. B. the velocity increases first and then decreases. C. the acceleration increases gradually. D. the acceleration decreases first and then increases

According to Newton's second law, the magnitude of acceleration increases gradually, and the direction of acceleration is downward, which is opposite to the velocity, then the velocity decreases gradually. So a and C are correct, B and D are wrong

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