题目
题型:不详难度:来源:
![](http://img.shitiku.com.cn/uploads/allimg/20191204/20191204162811-62348.gif)
答案
解析
设B物体的加速度为a2,A板的加速度为a1,分别由牛顿第二定律:
μm2g=m2a2 ············································································································ ①
F+μm2g=m1a1 ······································································································· ②
设B运动的位移为S2,A运动的位移为S1,经过t时间两者速度均为v,根据运动学公式:
SB=t ············································································································· ③
SA=t ·················································································································· ④
v=v0-a2t=a1t········································································································· ⑤
B在A上相对A向右运动的路程S=SB-SA ······································································ ⑥
联立①②③④⑤⑥解得:S=··············································································· ⑦
将F=1N,S=1m代入,解得:v0=4m/s
(2)根据⑦式分析可知,当1N≤F≤F1时,随着F力增大,S减小,当F=F1时,出现S突变,说明此时A、B在达到共同速度后,恰好再次发生相对运动,B将会从A板左端掉下。
对A、B恰好发生相对运动时,B的加速度为a2,则整体加速度也为a2,由牛顿第二定律:
F1=(m1+m2)a2········································································································ ⑧
联立①⑧解得解得F1=3N
(3)此时B在A上运动的路程为S1==m
当F≥F1时,物体B在A板上的路程为B相对A向右运动的路程的两倍。
故当F=F2时,将S=0.5S1代入⑦式解得:F2=9N
【评析】本题考查牛顿运动定律。滑块问题是物理模型中非常重要的模型,是学生物理建模能力培养的典型模型。滑块问题的解决非常灵活,针对受力分析、运动分析以及牛顿第二定律的掌握,还有相对运动的分析,特别是摩擦力的变化与转型,都是难点所在。本题通过非常规的图象来分析滑块的运动,能从图中读懂物体的运动。
核心考点
试题【如图(a)所示,在足够长的光滑水平面上,放置一长为L=1m、质量为m1=0.5kg的木板A,一质量为m2=1kg的小物体B以初速度v0滑上A的上表面的同时对A施】;主要考察你对牛顿第二定律及应用等知识点的理解。[详细]
举一反三
A.加速下降 | B.减速上升 |
C.匀速向右运动 | D.加速向左运动 |
![](http://img.shitiku.com.cn/uploads/allimg/20191204/20191204162801-90034.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191204/20191204162743-55146.jpg)
A.mc>mA,gc≠gA |
B.mc<mA,gc≠gA |
C.mc>mA,gc=gA |
D.mc<mA,gc=gA |
![](http://img.shitiku.com.cn/uploads/allimg/20191204/20191204162739-18319.jpg)
①、μa>μb,μa>μc ②、μa<μb,μa<μc ③、ma=mb,mc<ma
④、ma=mb,ma<mc
A.①④ | B.②④ | C.①③ | D.②③ |
![](http://img.shitiku.com.cn/uploads/allimg/20191204/20191204162724-36499.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191204/20191204162724-36499.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191204/20191204162724-85822.gif)
小题1:该物体的质量为多少?
小题2:在该物体上放一个与该物体质量相同的砝码,保持砝码与该物体相对静止,其他条件不变,请在图2的坐标上画出相应的a——F图线。
小题3:由图线还可以得到什么物理量?(要求写出相应的表达式或数值)选题理由:学会读图,利用图象处理问题
![](http://img.shitiku.com.cn/uploads/allimg/20191204/20191204162641-16392.gif)
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