Just like with the other force-related problems, we start with a free body diagram.

像所有其他电源问题一样， 我们从一个自由图开始。

To find out, first let's draw a free body diagram for the lift, making UP the positive direction.

为了找出答案，我们先画一个自由图 对于电梯，通过使正方向向上。