Mother asked her if she was very hot with so many clothes on中为什么要加on?

Mother asked her if she was very hot with so many clothes on中为什么要加on?

有具体的物品,必须加on
如果没有on,句子不对

on标示当时的状态

put on 是片语 固定搭配。

词组put on the clothes, on 表明衣服已经在身上