题目

Health experts have discovered that adding low-calorie vegetable soup to the start of a meal can actually help to lose weight. Because you feel full sooner, you eat less of your main course. The soup regime（养生法）was tested by researchers at Pennsylvania State University, led by Dr Barbara Rolls. They found that when people ate a first course of soup before lunch they reduced their total calorie intake by 20 per cent, compared with those who did not begin the meal with soup. But those who favor creamy soups should be careful．Researchers stressed the soup must be low-calorie and based列车关闭发动机进站，做匀减速直线运动，当滑行x1=300m时，速度减为一半，又滑行t2=20s停下．（1）作出列车运动的v-t图象．（2）求关闭发动机时列车的速度v0．（3）求列车滑行的总路程x．