As you come to the top of the building, the elevator has to decelerate, so that it loses its positive velocity and comes to rest.

当你要到顶时,电梯需要减速,此时电梯速度减小最后静止

耶鲁公开课 - 基础物理课程节选

You can see that if a was equal to g, your downward acceleration is that of gravity, namely the cable has snapped in the elevator, Then you don't feel any weight.

你会发现如果 a 等于 g,你下降的加速度就是重力加速度,也就是电梯的绳索断了,那时你会完全失重

耶鲁公开课 - 基础物理课程节选