问题 选择题

如图所示,质量均为m的甲、乙两同学,分别静止于水平地面的台秤P、Q上,他们用手分别竖直牵拉一只弹簧秤的两端,稳定后弹簧秤的示数为F,若弹簧秤的质量不计,下列说法正确的是(  )

A.甲受到的拉力大于F,乙受到的拉力小于F

B.台秤P的读数等于mg-F

C.台秤Q的读数为mg-2F

D.两台秤的读数之和为2mg

答案

A、甲受到的拉力与乙受到的拉力是作用力与反作用力,都等于F,故A错误;

B、对甲受力分析,甲受重力、支持力及弹簧秤向下的拉力,则有甲受到支持力为mg+F;故B错误;

C、对乙分析,乙受到的拉力向上,故台秤的示数为mg-F,故C错误;

D、将两人做为整体分析,整体受重力、支持力,故两台秤的示数之和为2mg;故D正确;

故选D.

阅读理解

D

Ellen Swallow Richards was the first woman to earn a bachelor’s degree from Massachusetts Institute of Technology (MIT). A chemist, social activist, teacher, and first woman member of the Institute of Engineering, she believed that housekeeping was a science. As a progressive thinker at the time, she thought that women needed to learn about money matters and have up-to-date information on cleanliness and nutrition. She encouraged women from all backgrounds to get the best education possible.

Ellen was born in 1842 and was brought up in Massachusetts. A graduate of Vassar College in New York, she returned to New England to attend MIT. After her marriage to Professor Robert Richards, she worked in a laboratory at MIT, examining pollution of water sources in Massachusetts. Her work led to the creation of the first food-inspection (检验) laws of that state. She was instructor at MIT from 1884 until her death in 1911.

Like other progressive thinkers of the time, Ellen was worried about problems of the poor and the effect of the environment on society. She considered the environment a key factor in quality of life. Within the family, as in the world at large, science was chief in tools used to help the poor. Science could help to manage money matters, keep a home safe and clean, and improve quality of life. Food properly cooked could be tasty, nutritious, and inexpensive. Better and cheaper food could protect the health and improve the lives of working-class families.

Ellen created the science of housekeeping, now called home economics, and elevated(提升)it to a serious college subject. She worked tirelessly as a national leader in developing standards, materials, and teacher training for this new field. Her publications cover many subjects—from the chemistry of cooking and cleaning to the cost of living.

57. According to the text, Ellen __________.

A. provided new jobs for the poor            B. helped to create new kinds of food

C. set up the field of home economics         D. created the ideas of food-inspection laws

58. As a progressive thinker, Ellen __________.

A. suggested people cook their own meals at home

B. believed cheap food was better than expensive one

C. advised women to get the best education possible

D. considered money matters a key factor in quality of life

59. Ellen believed that __________.

A. poor families knew how to manage money

B. families were well informed about good nutrition

C. cheaper food could not protect people’s health

D. families spent much on food but were not well nourished

60. One can infer that, as a result of the efforts of people such as Ellen, __________.

A. one may study home economics at a university for a career

B. the pollution of water sources is no longer a problem

C. most people today learn to cook at school

D. science does not help much within the family as in the world

单项选择题