如图所示，水平传送带以恒定的速度2m/s²向左运动，将物体（可视为质点）轻轻放在传送带的右端，经时间2s，物体速度变为2m/s²。再经过时间2s，物体到达传送带的左端。求：
（1）物体在水平传送带上滑动时的加速度大小；
（2）物体与水平传送带间的动摩擦因数；
（3）物体从水平传送带的右端到达左端通过的位移。
参考答案：
由题意可知，物体前2s内做匀加速度直线运动，后2s内做匀速直线运动。
设前2s内物体的位移为x1，对物体受力分析如图所示。
由牛顿第二定律得
①
由运动学公式得
②
③
设后内物体的位移为，则
④
物体从水平传送带的右端到达左端通过的位移
⑤
联立①②③④⑤式解得，
。
My dad was a fisherman. He worked hard and stayed out until he caught enough ______ to feed the family nearly every day. When the weather was bad he would ______ me to school. An old truck was used in his fishing business. When we got to the school, he would give me a big ________on the face and tell me to be a good _______. It was so embarrassing for me. I was 12 years old, and my dad would still kiss me goodbye! I remember the day when I decided I was too _______for a goodbye kiss. When we got to the school and came to a stop, he had his usual big smile. He started to lean 倾斜 toward me, but I put my hand up and ________, “No, Dad. ” It was the first time I had ever talked to him that way. He had a surprised look on his face for a long time, and his________started to be wet. He turned and looked out of the windshield 挡风玻璃. “You’re ______,” he said. “You are a big boy—a man. I won’t kiss you any more. ” It wasn’t long after that when my dad went out to ______and never came back. It was a day when most of the fishermen stayed at home except Dad. He had a big family to feed How I wish I had been a man then. If I had been a man, I would ________have told my dad I was too old for a goodbye kiss.
|