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why the answer is A and D?why not B?

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why the answer is A and D?why not B?
9,如右图所示,小球在竖直力F作用下将竖直弹簧压缩,若将力F撤去,小球将向上弹起并离开弹簧,直到速度变为零为止,在小球上升的过程中 ( )
A. 小球的动能先增大后减小
B.小球在离开弹簧时动能最大
c.小球的动能最大时弹性势能为零
D.小球的动能减为零时,重力势能最大
答案是AD
why the answer is A and D?why not B?
我明白了.
在弹簧恢复原长过程中,弹簧受到阻力源于小球重力,故在恢复原长过程中,弹簧与小球间始终有力的作用.
最开始,弹簧弹力大于小球重力,小球做加速运动.
后来,在一时刻,弹簧弹力与小球重力相等.
之后,弹簧弹力小于小球重力,小球做减速运动,而此时弹性势能不为0.
故无BC
the answer is A,tellme why ,why not use B the answer is A ,tell me why why not use B or C the answer is A,tell me why and translate it the answer is A ,tell me why and translate it the answer is A,why not use tell me why ,thanks Why the answer is the answer is B,tell me why the answer is B,tell my why the answer is a,WHY IN details IQ题:Why the answer is "A"? the answer is A,tell me why the answer is D,tell me why and trealate it ,thanks