题目

Tom arrived at the bus station quite early for Paris bus. The bus for Paris would not leave until five to twelve. He saw a lot of people waiting in the station. Some were standing in line, and others were walking around. There was a group of schoolgirls. Their teacher was trying to keep them in line. Tom looked around but there was no place for him to sit. He walked into the station cafe. He looked up at the clock there. It was only twenty to twelve. He found a seat and sat down before a large mirror on the wall. Just then, Mike, one of Tom’s workmates came in and sat with Tom. “Wha如图所示，粗细均匀的棒一端搁在地上，另一端与支点O连接．要求：（1）作出地面对棒的支持力和棒所受重力的示意图；（2）画出重力的力臂．