（1）选用天平、秒表和石块等器材，利用自由落体运动规律，可估_爱下问搜题

搜题请搜索小程序“爱下问搜题”

问题实验题

（1）选用天平、秒表和石块等器材，利用自由落体运动规律，可估测井口到水面的深度。若当地的重力加速度为，则：

①还需要测量的物理量是（选填：A、石块的质量 B、石块由井口下落到水面的时间）；

②可求得井口到水面的深度。

（2）右图所示，为“探究物体质量一定时，加速度与物体受力的关系”的实验装置示意图。

① 把长木板不带滑轮的一端垫高，其目的是；

（选填：A．平衡摩擦力 B．使得小车运动得更快一些）

② 电磁打点计时器应接；

（选填：A．低压直流电源 B．低压交流电源）

③ 如图所示，纸带记录的是某次实验过程中小车的运动情况，由刻度尺所测数据分析可知，小车做。

（选填：A．匀速直线运动 B．变速直线运动）

答案

（1）①B．石块由井口下落至水面的时间t（说明：答“B”或答“石块由井口下落至水面的时间t ”或“t”也得2分）；

②（说明：答“4．9t²”或“5t²”也得2分）。

（2）①A．平衡摩擦力（说明：答“A”或答“平衡摩擦力”也得2分）

②B．低压交流电源（说明：答“B”或答“交流电源”也得2分）

③A．匀速直线运动（说明：答“A”或答“匀速直线运动”也得2分）

题目分析：（1）①由自由落体运动规律可知需要测量t②由自由落体运动规律可知深度为（2）①本实验为了方便控制合力变化需要平衡掉摩擦力②电磁打点计时器应接低压交流电源③由运动轨迹发现在相等时间内通过的位移相同，判断做匀速直线运动

点评：本题难度较小，掌握自由落体运动规律和验证牛顿第二定律的实验原理不难回答本题

单项选择题

Questions 21-25We are not who we think we are.The American self-image is suffused with the golden glow of opportunity. We think of the United States as a land of unlimited possibility, not so much a classless society but as a place where class is mutable-a place where brains, energy and ambition are what counts, not the circumstances of one’s birth.The Economic Mobility Project, an ambitious research initiative led by Pew Charitable Trusts, looked at the economic fortunes of a large group of families over time, comparing the income of parents in the late 1960s with the income of their children in the late 1990s and early 2000s. Here is the finding: "The ’rags to riches’ story is much more common in Hollywood than on Main Street. Only 6 percent of children born to parents with family income at the very bottom move to the top.That is right, just 6 percent of children born to parents who ranked in the bottom fifth of the study sample, in terms of income, were able to bootstrap their way into the top fifth. Meanwhile, an incredible 42 percent of children born into that lowest quintile are still stuck at the bottom, having been unable to climb a single rung of the income ladder.It is noted that even in Britain-a nation we think of as burdened with a hidebound class system-children who are born poor have a better chance of moving up. When the three studies were released, most reporters focused on the finding that African-Americans born to middle-class or upper middle-class families are earning slightly less, in inflation-adjusted dollars, than did their parents.One of the studies indicates, in fact, that most of the financial gains white families have made in the past three decades can be attributed to the entry of white women into the labor force. This is much less true for African-Americans.The picture that emerges from all the quintiles, correlations and percentages is of a nation in which, overall, "the current generation of adults is better off than the previous one", as one of the studies notes.The median income of the families in the sample group was $55,600 in the late 1960s; their children’s median family income was measured at $71,900. However, this rising tide has not lifted all boats equally. The rich have seen far greater income gains than have the poor.Even more troubling is that our notion of America as the land of opportunity gets little support from the data. Americans move fairly easily up and down the middle rungs of the ladder, but there is "stickiness at the ends" - four out of ten children who are born poor will remain poor, and four out often who are born rich will stay rich.

It can be inferred from the undertone of the writer that America, as a classless society, should _______.

A．perfect its self-image as a land of opportunity

B．have a higher level of upward mobility than Britain

C．enable African-Americans to have exclusive access to well-paid employment

D．encourage the current generation to work as hard as the previous generation

判断题

海水的渗透压为血液的7~8倍。（）