小班讲义高一物理第10讲牛顿运动定律的应用3——受力=

1、龙 文 教 育精品小班课程辅导讲义讲义编号 2013秋季 辅导科目： 物理 年级： 高一课 题第10讲：牛顿运动定律的应用3受力=运动教学目标教学重点、难点教学内容一、已知受力情况确定运动情况1、牛顿第一定律： 牛顿第一定律定义了力：物体的运动不需要力来维持，力是改变运动状态的原因。2、牛顿第二定律： 牛顿第二定律确定了运动和力的关系，使我们能够把物体的运动情况与物体的受力情况联系起来。3、牛顿第三定律： 牛顿第三定律说明了作用力与反作用力之间的关系，把相互作用的几个物体联系起来了。例题1：一个静止在光滑水平地面上的物体，质量是2 kg，在6.4 n的水平拉力作用下沿水平地面向右运动。求物体在

2、4 s末的速度和4 s内的位移。（1）从题目中找出关于物理情景的描述。（2）研究对象是谁？它共受几个力的作用，画出受力图。合力沿什么方向？大小是多少？（3）物体的运动是匀变速运动吗？依据是什么？（4）完整写出解答过程。拓展一：例题1中如果物体与地面间的“动摩擦因数是0.21 ”。求物体在4s末的速度和4s内的位移，g=10m/s2。（1）物体受到的摩擦力应该怎样求？大小是多少？方向向哪？（2）画出受力图，写出解答过程。拓展二：将例题1中的“水平拉力”改为“斜向上与水平方向成37角”，大小仍为6.4 n，其他条件均不变，求物体在4 s末的速度和4 s内的位移。已知cos37=0.8，g=10m/

3、s2。（1）从题目中找出关于物理情景的描述。（2）研究对象是谁？它共受几个力的作用，画出受力图。合力沿什么方向？（3）拉力与运动方向成一定夹角时，如何求合力？（4）完整写出解答过程。拓展三：例题1中如果物体与地面间的“动摩擦因数是0.21 ”。将 “水平拉力”改为“斜向上与水平方向成37角”，大小仍为6.4 n，其他条件均不变，求物体在4 s末的速度和4 s内的位移。已知cos37=0.8，g=10m/s2。（1）从题目中找出关于物理情景的描述。（2）研究对象是谁？它共受几个力的作用，画出受力图。合力沿什么方向？（3）拉力与运动方向成一定夹角时，如何求合力？（4）完整写出解答过程。例题2、一斜

4、面ab长为10 ,倾角为,一质量为kg的小物体(大小不计)从斜面顶端a点由静止开始下滑,如图所示(取10 m/s2)(1) 若斜面与物体间光滑,求小物体下滑到斜面底端b点时的速度及所用时间.(2)若斜面与物体间的动摩擦因数为0.5,求小物体下滑到斜面底端b点时的速度及所用时间.二、已知运动情况确定受力情况1两类动力学问题（1）已知物体的受力情况，求物体的运动情况。（2）已知物体的运动情况，求物体的受力情况。2应用牛顿运动定律解决问题的一般思路（1）明确研究对象。（2）对研究对象进行受力情况分析，画出受力图。（3）以加速度的方向为正方向，与正方向相同的力为正，与正方向相反的力为负，列牛顿第二定律

5、的方程及其他相关方程。（4）解方程时，f、m、a都用国际单位制单位。3分析两类问题的基本方法（1）抓住受力情况和运动情况之间联系的桥梁加速度。力的合成分解受力情况f1、f2f合a受力情况v0、vt、s、t（2）分析流程图f合=ma运动学公式 （强调：牛顿第二定律是“桥梁”，受力分析和运动分析是基础，正交分解是方法。）例1、从静止开始做匀加速直线运动的汽车，经过t=10s，发生位移x=30m已知汽车的质量m=4103kg，牵引力f=5.2103n求：（1）汽车运动的加速度大小；（2）运动过程中汽车所受的阻力大小做一做：1、一辆质量为1000kg的小汽车正以10m/s的速度行驶，现在让它在12.5

6、m的距离内匀减速停下来，求所需阻力的大小。2、质量为40kg的物体静止在水平面上, 当在400n的水平拉力作用下由静止开始经过16m时, 速度为16 m/s, 求物体受到的阻力是多少?例题2、如图所示，质量为0.5kg的物体在与水平面成300角的拉力f作用下，沿水平桌面向右做直线运动，经过0.5m的距离速度由0.6m/s变为0.4m/s，已知物体与桌面间的动摩擦因数0.1，求作用力f的大小。（g10m/s2）做一做：3 一个滑雪的人，质量是75 kg，以v0=2 m/s的初速度沿山坡匀加速滑下，山坡的倾角=30，在t=5 s的时间内滑下的路程x=60 m，求滑雪人受到的阻力（包括摩擦和空气阻力

7、）。（1）从题目中找出关于物理情景的描述。（2）研究对象是谁？找出关于运动状态的描述。（3）求出人的加速度，并画出受力图。合力沿什么方向？大小是多少？（4）怎样求人受的阻力？完整写出解答过程。 第 10 次课后作业学生姓名： 1一个质量为21kg的物体同时受到两个力的作用,这两个力的大小分别为2n和6n,当两个力的方向发生变化时,物体的加速度大小可能为( )a.1m/s2 b.2m/s2 c.3m/s2 d.4m/s22、一个物体从离地面一定的高度由静止释放，如果下落过程中受到的空气阻力是物体重力的0.2倍，则物体下落的加速度大小是_m/s2。如果从地面上以一定的初速度竖直向上抛出一物体，受到

8、的空气阻力仍是重力的0.2倍，则物体上升时的加速度大小是_m/s2。（g取10 m/s2）3、一个静止在水平面上的物体，质量为2 kg，受水平拉力f=6 n的作用从静止开始运动，已知物体与平面间的动摩擦因数，求物体2 s末的速度及2 s内的位移。（g取10 m/s2）4、质量为20kg的物体若用20n的水平力牵引它，刚好能在水平面上匀速前进。求：（1）若改用50n拉力沿与水平方向成37的夹角向斜上方拉它，使物体由静止出发在水平面上前进2.3m时，它的速度多大？（2）在前进2.3m时撤去拉力，又经过3s，物体的速度多大？5、一个滑雪运动员沿与水平成30斜坡滑下，坡长400m，设下滑时运动员下滑时

9、没有使用滑雪杆，他受到的平均阻力（包括摩擦力和空气阻力）为下滑分力的1/5，求运动员从静止开始到达坡底时的速度和时间。6、 质量为1.5kg的物体在水平拉力f的作用下，从水平面上a点由静止开始运动，运动一段距离后撤去该力，物体继续滑行t2.0s停在b点，已知ab两点的距离l5.0m，物体与水平面间的动摩擦因数为0.20，求水平拉力f的大小?7、一架救灾直升机从距离地面16 m的高处让一箱物资由静止开始落下，经2 s物资落地，已知物资的质量为10 kg，它下落过程中所受空气阻力可认为大小不变。求空气阻力的大小。（取g=10 m/s2）（1）找出关于物理情景的描述。属于哪一类型的问题？解题的思路应

10、该是什么？（2）研究对象是谁？受几个力的作用，画出受力图。合力方向向哪？（3）写出解答过程。待添加的隐藏文字内容28、如图所示物体以初速沿斜面上滑时加速度大小为6m/s2，沿斜面自由下滑时加速度大小为4 m/s2，试求物体与斜面间的动摩擦因数以及斜面的倾角。m9、（2009江苏卷）航模兴趣小组设计出一架遥控飞行器，其质量m =2，动力系统提供的恒定升力f =28 n。试飞时，飞行器从地面由静止开始竖直上升。设飞行器飞行时所受的阻力大小不变，g取10m/s2。 （1）第一次试飞，飞行器飞行t1 = 8 s 时到达高度h = 64 m。求飞行器所阻力f的大小； （2）第二次试飞，飞行器飞行t2 =

11、 6 s 时遥控器出现故障，飞行器立即失去升力。求飞行器能达到的最大宽度h；winger tuivasa-sheck, who scored two tries in the kiwis 20-18 semi-final win over england, has been passed fit after a lower-leg injury, while slater has been named at full-back but is still recovering from a knee injury aggravated against usa.both sides boast 1

12、00% records heading into the encounter but australia have not conceded a try since josh charnleys effort in their first pool match against england on the opening day.aussie winger jarryd hayne is the competitions top try scorer with nine, closely followed by tuivasa-sheck with eight.but it is recent

13、ly named rugby league international federation player of the year sonny bill williams who has attracted the most interest in the tournament so far.the kiwi - with a tournament high 17 offloads - has the chance of becoming the first player to win the world cup in both rugby league and rugby union aft

14、er triumphing with the all blacks in 2011.id give every award back in a heartbeat just to get across the line this weekend, said williams.the (lack of) air up there watch mcayman islands-based webb, the head of fifas anti-racism taskforce, is in london for the football associations 150th anniversary

15、 celebrations and will attend citys premier league match at chelsea on sunday.i am going to be at the match tomorrow and i have asked to meet yaya toure, he told bbc sport.for me its about how he felt and i would like to speak to him first to find out what his experience was.uefa hasopened disciplin

16、ary proceedings against cskafor the racist behaviour of their fans duringcitys 2-1 win.michel platini, president of european footballs governing body, has also ordered an immediate investigation into the referees actions.cska said they were surprised and disappointed by toures complaint. in a statem

17、ent the russian side added: we found no racist insults from fans of cska. baumgartner the disappointing news: mission aborted.the supersonic descent could happen as early as sunda.the weather plays an important role in this mission. starting at the ground, conditions have to be very calm - winds les

18、s than 2 mph, with no precipitation or humidity and limited cloud cover. the balloon, with capsule attached, will move through the lower level of the atmosphere (the troposphere) where our day-to-day weather lives. it will climb higher than the tip of mount everest (5.5 miles/8.85 kilometers), drift

19、ing even higher than the cruising altitude of commercial airliners (5.6 miles/9.17 kilometers) and into the stratosphere. as he crosses the boundary layer (called the tropopause),e can expect a lot of turbulence.the balloon will slowly drift to the edge of space at 120,000 feet ( then, i would assum

20、e, he will slowly step out onto something resembling an olympic diving platform.they blew it in 2008 when they got caught cold in the final and they will not make the same mistake against the kiwis in manchester.five years ago they cruised through to the final and so far history has repeated itself

21、here - the last try they conceded was scored by englands josh charnley in the opening game of the tournament.that could be classed as a weakness, a team under-cooked - but i have been impressed by the kangaroos focus in their games since then.they have been concentrating on the sort of stuff that wi

22、ns you tough, even contests - strong defence, especially on their own goal-line, completing sets and a good kick-chase. theyve been great at all the unglamorous stuff that often goes unnoticed in the stands but not by your team-mates.it is as though their entire tournament has been preparation for t

23、he final.in johnathan thurston, cooper cronk, cameron smith and either billy slater or greg inglis at full-back they have a spine that is unmatched in rugby league. they have played in so many high-pressure games - a priceless asset going into saturday.the kiwis are a lot less experienced but winnin

24、g a dramatic match like their semi-final against england will do wonders for their confidence.they defeated australia in the four nations final in 2010 and the last world cup, and know they can rise to the big occasion.winger tuivasa-sheck, who scored two tries in the kiwis 20-18 semi-final win over

25、 england, has been passed fit after a lower-leg injury, while slater has been named at full-back but is still recovering from a knee injury aggravated against usa.both sides boast 100% records heading into the encounter but australia have not conceded a try since josh charnleys effort in their first

26、 pool match against england on the opening day.aussie winger jarryd hayne is the competitions top try scorer with nine, closely followed by tuivasa-sheck with eight.but it is recently named rugby league international federation player of the year sonny bill williams who has attracted the most intere

27、st in the tournament so far.the kiwi - with a tournament high 17 offloads - has the chance of becoming the first player to win the world cup in both rugby league and rugby union after triumphing with the all blacks in 2011.id give every award back in a heartbeat just to get across the line this week

28、end, said williams.the (lack of) air up there watch mcayman islands-based webb, the head of fifas anti-racism taskforce, is in london for the football associations 150th anniversary celebrations and will attend citys premier league match at chelsea on sunday.i am going to be at the match tomorrow an

29、d i have asked to meet yaya toure, he told bbc sport.for me its about how he felt and i would like to speak to him first to find out what his experience was.uefa hasopened disciplinary proceedings against cskafor the racist behaviour of their fans duringcitys 2-1 win.michel platini, president of eur

30、opean footballs governing body, has also ordered an immediate investigation into the referees actions.cska said they were surprised and disappointed by toures complaint. in a statement the russian side added: we found no racist insults from fans of cska. baumgartner the disappointing news: mission a

31、borted.the supersonic descent could happen as early as sunda.the weather plays an important role in this mission. starting at the ground, conditions have to be very calm - winds less than 2 mph, with no precipitation or humidity and limited cloud cover. the balloon, with capsule attached, will move

32、through the lower level of the atmosphere (the troposphere) where our day-to-day weather lives. it will climb higher than the tip of mount everest (5.5 miles/8.85 kilometers), drifting even higher than the cruising altitude of commercial airliners (5.6 miles/9.17 kilometers) and into the stratospher

33、e. as he crosses the boundary layer (called the tropopause),e can expect a lot of turbulence.the balloon will slowly drift to the edge of space at 120,000 feet ( then, i would assume, he will slowly step out onto something resembling an olympic diving platform.they blew it in 2008 when they got caught cold in the final and they will not make the same mistake against the kiwis in manchester.five years ago they cruised through to the final and so far history has repeated itself