图中弹簧秤、绳和滑轮的质量均不计，绳与滑轮间的摩擦力不计，物_爱下问搜题

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问题选择题

图中弹簧秤、绳和滑轮的质量均不计，绳与滑轮间的摩擦力不计，物体的重力都是G，在图甲、乙、丙三种情况下，弹簧秤的读数分别是F₁、F₂、F₃，则

A．

B．

C．

D．

答案

答案：B

题目分析：甲图：物体静止，弹簧的拉力；乙图：对物体为研究对象，作出力图如图．由平衡条件得，丙图：以动滑轮为研究对象，受力如图．由几何知识得，B正确，

点评：本题是简单的力平衡问题，关键是分析物体的受力情况，作出力图．对于丙图，是平衡中的特例，结果要记忆．

完形填空

This is a part from US President Barack Obama’s speech on May 14 at Bamard College in New York.
… My last piece of advice – this is simple, but perhaps most important: 36. Nothing worthwhile is easy. No one of achievement has avoided failure – sometimes catastrophic failures. But they keep at it. They learn from mistakes. They don’t 37.
When I first arrived on this 38, I was with little money, fewer options. But it was here that I tried to find my place in this world. I knew I wanted to make a difference, but it was 39 how in fact I’d go about it. But I wanted to do my part to 40 a better world.
So even as I worked after graduation in a few 41 jobs here in New York, even as I went from motley (鱼龙混杂的)apartment to motley apartment, I 42.
… And I wish I could say that this perseverance came from some innate (天生的)toughness in me. But the truth is, it was 43. I got it from 44 the people who raised me. I grew up as the son of a single mom who struggled to put herself through 45 and make ends meet. She had a marriage that fell apart; 46 went on food stamps at one point to help us 47. But she didn’t quit. And she earned her degree, and made sure that 48 scholarships and hard work, my sister and I earned 49.
And 50, I met a woman who was assigned to advise me on my first summer job at a law firm. And she gave me such good advice that I married her. And Michelle and I gave everything we had to balance our careers and a 51 family. We made that marriage work.
… So 52 it’s starting a business, or running for office, or 53 an amazing family, remember that making your 54 on the world is hard. It takes patience. It takes commitment. It comes with plenty of 55 and it comes with plenty of failures.

D．preservation

D．unsatisfactory

A．reached out

A．for the time being

B．long before

C．shortcomings

判断题

积分调节的缺点是有滞后作用。