题目内容


在学习运动的合成与分解时我们做过如图所示的实验．在长约80cm～100cm一端封闭的玻璃管中注满清水，水中放一个用红蜡做成的小圆柱体（小圆柱体恰能在管中匀速上浮），将玻璃管的开口端用胶塞塞紧，然后将玻璃管竖直倒置，在红蜡块匀速上浮的同时使玻璃管紧贴黑板面在水平方向上匀加速移动，你正对黑板面将看到红蜡块相对于黑板面的移动轨迹可能是下列选项中的（                                                                             ）                     

                                                                                                             

　  A．                  B．                         C．      D．

                                                                                                                                 


C

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如图所示，三块重均为3N的完全相同的光滑棋子A        B             C，B和C叠放在一起由竖直弹簧支持，初态静止．现将A由静止放到B上．则在A放到B上瞬间．（g=10m/s2）（              ）                            

                                                                                                                 

　   A． A对B的压力为2N  B．      B对C的压力为3N

　   C． B的加速度为5m/s2  D．     C的加速度为零

                                                                                                                                     


如图所示，斜面为长方形的斜面体倾角为37°，其长为0.8m，宽为0.6m．一重为20N的木块原先在斜面体上部，当对它施加平行于AB边的恒力F时，刚好使木块沿对角线AC匀速下滑，求木块与斜面间的动摩擦因数μ和恒力F的大小．                                                                                                                                   

                                                                               

                                                                                                                                   


一小组用如图所示装置测定滑块与斜面间的动摩擦因数．斜面下端固定一光电门，上端由静止释放一带有遮光条的滑块，滑块沿斜面加速通过光电门．                                                                                          

（1）要测量木板与斜面间的动摩擦因数，除了已知当地重力加速度g及遮光条宽度d、遮光时间t，还应测量的物理量是下列选项中的                                                                                 ；                                  

A．滑块的长度L                                                                                                              

B．斜面的倾角θ                                                                                                              

C．滑块的质量m                                                                                                             

D．释放滑块时遮光条到光电门间的距离x                                                                       

（2）用上述物理量表示滑块与斜面间动摩擦因数μ=                            ．                            

                                                                                            

                                                                                                                                        


如图所示，用传送带向高处运送货物．当货物在传送带上随传送带一起加速上行时，加速度大小为a1，货物受到的摩擦力大小为f1；在上行过程中传送带因故突然停住不动后的瞬间，货物加速度大小为a2，受到的摩擦力大小为f2．若货物与传送带间的最大静摩擦力等于滑动摩擦力．以下关系式可能正确的是（   ）                     

                                                                                                     

　   A．              a1＜a2，f 1＜f2    B． a1=a2，f 1=f2 C． a1＞a2，f 1＞f2      D． a1＜a2，f 1＞f2

                                                                                                                                  


如图甲所示，质量m=2kg的物体在水平面上向右做直线运动．过a点时给物体作用一个水平向左的恒力F并开始计时，选水平向右为速度的正方向，通过速度传感器测出物体的瞬时速度，所得v﹣t图象如图乙所示．取重力加速度为g=10m/s2．求：                                                                                                                                 

（1）物体在0﹣4s内和4﹣10s内的加速度的大小和方向                                           

（2）力F的大小和物体与水平面间的动摩擦因数μ                                                   

（3）10s末物体离a点的距离                                                                                    

（4）10s后撤去拉力F，求物体再过15s离a点的距离                                               

                        

                                                                                                                                 


用如图所示的计时装置可以近似测出气垫导轨上滑块的瞬时速度．已知固定在滑块上的遮光条的宽度为4.0mm，遮光条经过光电门的遮光时间为0.040s．则滑块经过光电门位置时的速度大小为（                 ）                     

                                                                                                              

　 A．  0.10m/s     B． 100m/s   C． 4.0m/s    D． 0.40m/s

                                                                                                                                        


如图所示，ABC为一固定的半圆形轨道，轨道半径R=0.4m，A、C两点在同一水平面上．现从A点正上方h=2m的地方以v0=4m/s的初速度竖直向下抛出一质量m=2kg的小球（可视为质点），小球刚好从A点进入半圆轨道．不计空气阻力，重力加速度g取10m/s2．                                                                                                         

（1）若轨道光滑，求小球下落到最低点B时的速度大小；                                                         

（2）若轨道光滑，求小球相对C点上升的最大高度；                                                         

（3）实际发现小球从C点飞出后相对C点上升的最大高度为h′=2.5m，求小球在半圆轨道上克服摩擦力所做的功．                                                                                                                                            

                                                                                                

                                                                                                                                        


质量为m的体操运动员，双手握住单杠，双臂竖直，悬吊在单杠下．当他如图增大双手间距离时（   ）   

                                                                

　   A．  每只手臂的拉力将减小

　   B．  两只手臂的拉力总是大小相等、方向相反

　   C．  每只手臂的拉力一定小于mg

　   D．  每只手臂的拉力可能等于mg

                                                                                                

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