题目

如图所示，质量为的滑块，以的水平初速度滑上静止在光滑水平面的平板小车，小车质量且足够长。求：滑块与小车的共同速度v；整个运动过程中系统产生的热量Q。 答案：【答案】（1） ，（2）40J【解析】滑块和小车组成的系统动量守恒，根据动量守恒定律求出滑块与小车的共同速度v。根据能量守恒定律求出整个过程中产生的热量Q。设滑块与小车共同速度为v，滑块的质量为m，原来的速度为，小车质量为M，取向右为正方向，根据动量守恒定律得：代入数值解得：根据阅读下面短文，根据短文内容完成表格中所缺信息，每空一词。In today’s society, everyone is busy and running at a fast pace every day. We feel our time is valuable and needs to be used well. We need cheap meal ideas that can help us save time and money and still provide a healthy and nutritious (有营养的) dinner for us and our family.The fast food makers know we have little time and that the idea of cooking dinner after a long day at work is not something we look forward to. So the fast food makers offer us cheap food that requires no cooking, no cleaning, and only 25 minutes to pick up.But eating so much fast food will cause body fatness and fast food is not nutritious, so it’s not the healthiest choice to consider. There are some very cheap meal ideas that take almost no time to prepare and will make coming home for a good meal more enjoyable.The first cheap meal idea is one dish which includes meat, vegetables and rice. This is not only a cheap meal idea, but also it is fast because it can be made in only 20 minutes.You can quickly make some pancakes and scrambled eggs for the family in about 30 minutes. If you think it is strange to eat breakfast food for dinner, consider how the same foods give you what you need to go through a whole day.Another cheap meal idea to try is a “macaroni and cheese with meat” dish, which only takes around 20 minutes to cook.If you are interested in these cheap meal ideas, you’re welcome to visit our website for details. When you fix one of these or other cheap meal ideas at home, you are taking time out of your busy day to treat yourself and your family in a special way.Ideas about cheap mealsFacts·____1.______life and valuable time·Being in need of cheap ,____ 2.____ and nutritious meals____3._____ of fast food·No cooking·No cleaning·No_____4.____timeDisadvantages of fast food·Making people get_____5.______·Having no nutritionThree__6.___of cooking·A dish______7._____meat, vegetables and rice_____8.___only 20 minutes·Pancakes and scrambled eggstaking around__9._____minutes·Macaroni and ____10.____with meattaking about 20 minutes