试说明图中几种情况下系统的运行状态是加速？减速？还是匀速？（图中箭头方向为转矩的实际作用方向）<br /> <img src="https://nimg.ppkao.com/2017-10/wangjinchen/2017101614504710717.jpg?sign=c30c9c0f253d406261651a0bb0b1a60b&t=62d0fbbc" />