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＞＞＞一个物体在两个互为锐角的恒力作用下，由静止开始运动，当经过一..
一个物体在两个互为锐角的恒力作用下，由静止开始运动，当经过一段时间后，突然去掉其中一个力，则物体将做(&&&&& )A．匀变速直线运动B．匀速运动C．匀速圆周运动D．匀变速曲线运动
题型：单选题难度：中档来源：不详
D试题分析：撤去一个力后，合力与速度不共线，故开始做曲线运动，由于合力为恒力，故加速度恒定，即做匀变速曲线运动；故选D．点评：关键是知道撤去一个力后，速度方向和合力方向不共线．
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据魔方格专家权威分析，试题“一个物体在两个互为锐角的恒力作用下，由静止开始运动，当经过一..”主要考查你对&&斜抛运动&&等考点的理解。关于这些考点的“档案”如下：
现在没空？点击收藏，以后再看。
因为篇幅有限，只列出部分考点，详细请访问。
斜抛的定义：
将物体以一定的初速度沿斜向上(或斜向下)抛出，物体仅在重力作用下所做的运动。斜抛的特性：
速度：水平方向 ，竖直方向位移：水平方向，竖直方向或对称性：①轨迹关于通过最高点的竖直线对称。&&&&&&&&&& &&&& ②同一高度速率相等。&&&&&&&&&&&&&&& ③从某一点到最高点的时间与从最高点下降至该高度的时间相等。斜抛的知识点拨：
斜抛运动是a=g的匀变速曲线运动。只受重力作用，且方向既不水平也不竖直。其运动可分解为水平方向上的匀速直线运动，和竖直方向上的竖直上抛或竖直下抛运动。斜抛运动：
①水平方向②竖直方向③斜抛运动时间：④小球能达到的最大高度（Y）叫做射高；从抛出点到落地点的水平距离（X）叫做射程。射高y=v02sin2θ/2g，射程X=2v02sinθcosθ/g。控制变量v0不变，θ=45°时，射程最大X=v02/g。
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& 英语：Unit4 Task课件（牛津译林版选修8）
英语：Unit4 Task课件（牛津译林版选修8）
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Task Writing a speech about the film industry Unit
4 Films and film events General introduction: The Task is divided into three steps and each step is preceded with a skills building activity. Through the three steps, you will learn how to complete a quiz, how to listen for emphasis and how to use information from more than one source.
Skills building 1: completing a quiz What should we do when we take a quiz? What steps we should take to make sure that we answer the questions correctly?
Step 1: completing a quiz about the film industry Listen to two radio programmes discussing the early days of film. Read a web page about film facts.
Use all of the information to complete a film quiz.
Answers to part A: 1. The Lumière brothers. 3. Moving pictures. 4. London. 5. The speed, the sound and the
color of the film. 8. In the theatre. 9. The Jazz Singer. 10. No idea.
Listen to another radio programme in Part B
This time you will listen to some information about Hollywood, and you can use the information to answer some of the remaining questions on the quiz.
Answers to part B: 7. The company with sound stages
and the place where the
company makes its films. 11. A few years. 12. Pre-production stage and post-
production stage.
Read the web page in Part C to find the remaining information and finish the quiz.
2. He said, ‘Cinema… has no commercial future.’ 6. $10,000,000. 13. 20th Century Fox, Universal Studios, Warner Bros and MGM.
Skills building 2: listening for emphasis In the Grammar and usage section, we learnt how to emphasize some parts of sentences by adding some words or using certain sentence structures.
Are there any other ways that we can emphasize some words or information, especially when we are speaking?
Step 2: asking and answering questions about Chinese films work in pairs to conduct an interview about Chinese films asking and answering questions about Chinese film
Skills building 3:
using information from more than one source What will you do before you attend a speech or an essay competition?
know what the subject of the competition is find out different aspects of the subject and write the draft do research on the aspects that you do not know Review what you have learnt about the film industry in Steps 1 and 2.
List the information you have already obtained. Think about what else you will need in making the speech or writing the essay for the competition.
For example:
The information I have already got: the first film-maker/ fa where the the first studio in H the title of the first ‘talking film’; the title of the first film made in C the differences between old and modern films
The information I need to do research on: the titles of the best films in some famous film some famous actors/ actresses in Hollywood/ China Step 3: writing a speech about the film industry write a speech using information gathered in the previous steps.
work in groups to discuss what you should write and how to write the speech Possible example
Ladies and gentlemen,
What I want to talk about here is the history of the film industry.
There are many firsts in the history of the film industry. Do you know when and where the first film was made? It was in the 1880s, more than 120 years ago, that William Friese-Green recorded and then played back what we now think of as a film. He made his film in Hyde Park, London, and later watched it in his home.
The fathers of modern film are thought to be the Lumière brothers from France. The first films ever made were silent. The audiences could hear different kinds of music played by a piano player or an orchestra in the theatre. It was not until in 1927 that the first ‘talking film’ or film with sound was shown in New York. The title of it was The Jazz Singer. Just imagine how audiences reacted when they watched the first film with sound! It is said that the audience was so excited that everyone in the theatre stood up and applauded.
In 1896, film was introduced to China. The first Chinese film ever made, Conquering Jun Mountain, was made in 1905. the first film made only by Chinese was The Difficult Couple, which was made in 1913. Then, about 18 years later, the first ‘talking film’ was made in China in 1931. The title of the film is The Songstress, Red Peony.
Although the first cinema that opened in the USA was in Pennsylvania, Hollywood is well known for film-making. Three quarters of the films seen around the world are made in the USA, and about ninety-nine per cent of them are made in Hollywood. The companies there make films in their studios. Do you know the name of the first studio that opened in Hollywood? It was Nestro Studios, which is now a part of Universal studios.
Language points 1. When completing a quiz, you must be certain that all the answers you write are correct. (P58) completing 现在分词做状语，因句子的主语是you, complete的逻辑主语也是you，两者是主动关系。 When __________ different cultures, we often pay attention only to the differences without noticing the many similarities.
A. compared
B. being compared
C. comparing
D. having compared
练习 certain adj.
肯定的，有把握的
1) Are you absolutely certain (that) you
gave them the right number?2) I feel certain (that) you’re doing the
right thing.3) You should make certain (that)
everyone understands the
instructions.4) I’m not certain how much it will cost. 2. You do not want the judge to misunderstand your answer because you have left out some words! (P58)
leave sb./sth. out
遗漏，忽视
1) You can leave the butter out of this
recipe if you’re on a low-fat diet.2) I’ve made a list of names—I hope I
haven’t left anyone out. 3. No figures are available for money made from popcorn sales, but film fans usually consume a lot of this salty snack, especially when watching a tense thriller. (P59)
adj. able to be obtained, used, or reached:Is this dress available in a larger size?Do you have any double rooms available this weekend? consume
v. [T] 1) to use fuel, energy or time, especially in large amounts:Our high living standards cause our present population to consume 25 percent of the world’s oil.2) to eat or drink, especially a lot of sth.:He consumes vast quantities of chips with every meal. 4. You have successfully entered the competition and want to include the information about the Chinese film industry in your speech. (P60)
v. [I or T] to be included in a competition, race or exam, or to arrange for someone else to do this:Are you going to enter the photography competition?
v. [T] to contain sth. as a part of sth. else, or to make sth. part of sth. else:The bill includes tax and service. 5. Speech and essay competitions often require you to do research on many different aspects of a subject. (P61)
to need or make necessary:require相关短语 require sth.
需要某物 require doing= require to be done
需要做 require sb. to do sth.
要求某人做某事 require sth. of sb.
要求某人某物 require that sb. should do
要求或命令某人做
1. Look at your shirt! It requires
__________.
A. washing
C. to wash
D. being washed 2. He will agree to do what you
require __________ him.
D. for aspect
noun [C] 方面 　1) Which aspects of the job do you
most enjoy? 2) His illness affects almost every
aspect of his life. 3) Have you thought about the
problem from every aspect? Homework
Finish your speech after
class. 2. Prepare for the Project Part.
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一个物体在水平方向的两个恒力作用下沿水平方向做匀速直线运动,若撤去其中的一个力,则（）A物体动能可能减少 B动能可能不变 C动能可能增加 D余下的力一定对物体做功
A物体动能可能减少 B动能可能不变 C动能可能增加 D余下的力一定对物体做功
答案选A,C、D设左右两个相等力,球向左走,当撤掉向左的力,那么向右的力与运动方向相反.球速减少,故动能减少.同理,若是撤掉向右的力,球速增加,动能增加.B不对原因：球受合外力不为零必然是对球做功了.然后球的重力势能等其他能不变,必然是动能改变了.D正确.物体只受一个力时,余下的力肯定对他做功希望帮得上忙
ACD,B错误力与速度的夹角不管是多少度，速度的大小总是改变
选ACD侧掉一个力后，物体的合力不在为0,所以物体的动能肯定在发生变化。那动能是变大还是变小呢，都有可能，因为当力与原来速度方向的夹角小于90度时力做正功，大于90度则做负功。如图，物体受到相互垂直的两个水平恒力F1和F2作用，并沿光滑水平面从A运动到B，发生的位移为S，AB连线与F1夹角为α，则这两个力对物体做功的表达式正确的是（　　）A．（F1+F2）SB．（F1-F2）SC．F1Scosα+F2SsinαD．F1Ssinα+F2S&cosα【考点】．【专题】功的计算专题．【分析】根据功的定义式W=Flosθ求解恒力做功．功是标量，几个力对物体做的总功，就等于各个力单独对物体做功的代数和．【解答】解：物体受到两个水平恒力F1&和F2作用，F1和F2互相垂直，物体沿光滑水平面从A点运动到B点的过程中，位移为s，AB连线与F1间的夹角为α，所以恒力F1&做功W1=F1scosα恒力F2&做功W2=F2ssin&α当有多个力对物体做功的时候，总功的大小就等于用各个力对物体做功的和，所以总功W=F1scos&α+F2ssin&α故选：C．【点评】因为功是标量，求标量的和，几个量直接相加即可．声明：本试题解析著作权属菁优网所有，未经书面同意，不得复制发布。答题：　难度：0.72真题：1组卷：0
解析质量好中差质量相等的A、B两物体（均可视为质点）放在同一水平面上，分别受到水平恒力F1、F2的作用，同时由静止开始从同一位置出发沿同一直线做匀加速运动．经过时间t0和4t0速度分别达到2v0和v0时分别撤去F1和F2，以后物体继续做匀减速运动直至停止．两物体速度随时间变化的图线如图所示．对于上述过程下列说法中正确的是（　　）-乐乐题库
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质量相等的A、B两物体（均可视为质点）放在同一水平面上，分别受到水平恒力F1、F2的作用，同时由静止开始从同一位置出发沿同一直线做匀加速运动．经过时间&t0和&4t0速度分别达到2v0和v0时分别撤去F1和F2，以后物体继续做匀减速运动直至停止．两物体速度随时间变化的图线如图所示．对于上述过程下列说法中正确的是（　　）F1和F2的大小之比为8：1A、B的位移大小之比为2：1在2t0和3t0间的某一时刻B追上AF1和F2的冲量大小之比为3：5
本题难度：一般
题型：单选题&|&来源：网络
分析与解答
习题“质量相等的A、B两物体（均可视为质点）放在同一水平面上，分别受到水平恒力F1、F2的作用，同时由静止开始从同一位置出发沿同一直线做匀加速运动．经过时间t0和4t0速度分别达到2v0和v0时分别撤去F1和F2，以...”的分析与解答如下所示：
A、根据两物块做匀减速运动，求出匀减速运动的加速度之比，从而求出摩擦力之比，再根据匀加速运动的加速度之比，根据牛顿第二定律求出F1和F2的大小之比．B、速度时间图线与时间轴所围成的面积表示位移．根据面积比得出位移比．C、B追上A时，两者位移相等，从图象上去分析在在2t0和3t0间位移是否相等，判断B有无追上A．D、根据I=Ft去求冲量大小之比．
解：A、从图象可知，两物块匀减速运动的加速度大小之都为v0t0，根据牛顿第二定律，匀减速运动中有f=ma′，则摩擦力大小都为mv0t0．根据图象知，匀加速运动的加速度分别为：2v0t0，v04t0，根据牛顿第二定律，匀加速运动中有F-f=ma，则F1=3mv0t0，F2=5mv04t0，F1和F2的大小之比为12：5．故A错误．&& B、图线与时间轴所围成的面积表示运动的位移，则位移之比为6：5．故B错误．&& C、在3t0末，A的位移大于B的位移，此时B未追上A．故C错误．&& D、根据I=Ft得，F1和F2的大小之比为12：5．作用时间之比为1：4，则冲量大小之比3：5．故D正确．故选D．
解决本题的关键通过图象得出匀加速运动和匀减速运动的加速度，根据牛顿第二定律，得出两个力的大小之比，以及知道速度-时间图线与时间轴所围成的面积表示位移．
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质量相等的A、B两物体（均可视为质点）放在同一水平面上，分别受到水平恒力F1、F2的作用，同时由静止开始从同一位置出发沿同一直线做匀加速运动．经过时间t0和4t0速度分别达到2v0和v0时分别撤去F1...
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经过分析，习题“质量相等的A、B两物体（均可视为质点）放在同一水平面上，分别受到水平恒力F1、F2的作用，同时由静止开始从同一位置出发沿同一直线做匀加速运动．经过时间t0和4t0速度分别达到2v0和v0时分别撤去F1和F2，以...”主要考察你对“牛顿第二定律”
等考点的理解。
因为篇幅有限，只列出部分考点，详细请访问。
牛顿第二定律
与“质量相等的A、B两物体（均可视为质点）放在同一水平面上，分别受到水平恒力F1、F2的作用，同时由静止开始从同一位置出发沿同一直线做匀加速运动．经过时间t0和4t0速度分别达到2v0和v0时分别撤去F1和F2，以...”相似的题目：
从F=ma可以导出m=Fa，可见物体的质量（　　）跟合外力成正比跟加速度成反比跟合外力与加速度均无关以上三点均不正确
如图所示，一物体沿固定的粗糙斜面向上滑动，在图中作出物体上滑过程中的受力示意图，并标明物体加速度方向．
如图所示，轻质弹簧连接A、B两物体，A用水平木板托住，B的上端通过细线挂在天花板上；已知A的质量为2kg、B的质量为1kg、弹簧的弹力为4N．在撤去木板的瞬间A的加速度可能是（　　）10&m/s28m/s212m/s20
“质量相等的A、B两物体（均可视为质点）放...”的最新评论
该知识点好题
1（2013o浙江）如图所示，水平板上有质量m=1.0kg的物块，受到随时间t变化的水平拉力F作用，用力传感器测出相应时刻物块所受摩擦力Ff的大小．取重力加速度g=10m/s2．下列判断正确的是（　　）
2一质点受多个力的作用，处于静止状态，现使其中一个力的大小逐渐减小到零，再沿原方向逐渐恢复到原来的大小．在此过程中，其它力保持不变，则质点的加速度大小a和速度大小v的变化情况是（　　）
3（2013o安徽）如图所示，细线的一端系一质量为m的小球，另一端固定在倾角为θ的光滑斜面体顶端，细线与斜面平行．在斜面体以加速度a水平向右做匀加速直线运动的过程中，小球始终静止在斜面上，小球受到细线的拉力T和斜面的支持力为FN分别为（重力加速度为g）（　　）
该知识点易错题
1（2012o上海）如图，质量分别为mA和mB的两小球带有同种电荷，电荷量分别为qA和qB，用绝缘细线悬挂在天花板上．平衡时，两小球恰处于同一水平位置，细线与竖直方向间夹角分别为θ1与θ2（θ1＞θ2）．两小球突然失去各自所带电荷后开始摆动，最大速度分别为vA和vB，最大动能分别为EkA和EkB．则（　　）
2（2012o安徽）如图所示，放在固定斜面上的物块以加速度a沿斜面匀加速下滑，若在物块上再施加一竖直向下的恒力F，则（　　）
3（2012o安徽）如图所示，在竖直平面内有一个半径为R的圆弧轨道．半径OA水平、OB竖直，一个质量为m的小球自A正上方P点由静止开始自由下落，小球沿轨道到达最高点B时恰好对轨道没有压力，已知AP=2R，重力加速度为g，则小球从P到B的运动过程中（　　）
欢迎来到乐乐题库，查看习题“质量相等的A、B两物体（均可视为质点）放在同一水平面上，分别受到水平恒力F1、F2的作用，同时由静止开始从同一位置出发沿同一直线做匀加速运动．经过时间t0和4t0速度分别达到2v0和v0时分别撤去F1和F2，以后物体继续做匀减速运动直至停止．两物体速度随时间变化的图线如图所示．对于上述过程下列说法中正确的是（　　）”的答案、考点梳理，并查找与习题“质量相等的A、B两物体（均可视为质点）放在同一水平面上，分别受到水平恒力F1、F2的作用，同时由静止开始从同一位置出发沿同一直线做匀加速运动．经过时间t0和4t0速度分别达到2v0和v0时分别撤去F1和F2，以后物体继续做匀减速运动直至停止．两物体速度随时间变化的图线如图所示．对于上述过程下列说法中正确的是（　　）”相似的习题。}