问题 问答题

小强为课题研究小组提供了一把家中收藏的旧杆秤.杆秤的刻度模糊不清,只有5kg和6kg的刻度清晰可辨,秤砣遗失.小组成员对杆秤的外形进行了测量,测量结果如图所示.请根据以上信息

(1)判断该杆秤的重心(不包括秤砣)应该在提纽的哪一侧;

(2)求出秤砣的质量.

答案

(1)从图可知,5kg到6kg质量增加了1kg,而杠杆的长增加了2cm,杆秤上的刻度是均匀的,所以,从0刻度线到5kg的位置,杠杆的长应该为10cm,即零刻度线在提纽的右侧,所以该杆秤的重心应该在提纽的左侧.(因为0刻度线处要挂称砣才能使杠杆在水平位置平衡) 

(2)我们用杆秤称物体时,物体在提纽的左侧,秤砣在提纽的右侧,该杆秤的重心在提纽的左侧,

设杆秤的重心到提纽的距离为S,秤砣的质量为m,杆秤的质量为m

由杠杆的平衡条件GL=GL可知,

∴5kg×g×3cm+m×g×S=m×g×11cm,

6kg×g×3cm+m×g×S=m×g×(11cm+2cm),

化简得:5kg×3cm+m×S=m×11cm,①

6kg×3cm+m×S=m×(11cm+2cm),②

解①②可得:m=1.5kg.

答:(1)判断该杆秤的重心应该在提纽的左侧.(2)秤砣的质量为1.5kg.

填空题


A Sports体育运动
Many animals engage in play,but homo sapiens is the only animal (1) have invented sports.Since sports are an invention,a part of culture (2) than an aspect of nature,all definitions of sports are somewhat arbitrary. (3) sports are a human universal found in every known culture or a (4) unique to modern society depends upon one’s definition of sports.Men and (5) have always run,jumped,climbed,lifted,thrown, and wrestled,but they have (6) always performed these physical activities competitively. Although all literate societies seem to (7) contests of one sort or another in which men, and sometimes women, (8) in displays and tests of physical skill and prowess,sports may be (9) defined as physical contests performed for their own sake and not for (10) ulterior end.According to this strict definition,neither Neolithic hunters nor contestants (11) religious ceremonies such as the ancient Olympic Games were engaged in sports. (12) on the stipulation that sports must be performed for their own sake (13) the paradoxical elimination of many activities which are usually thought of as (14) ,such as exercises done for the sake of cardiovascular fitness,races run (15) satisfy a physical education requirement,ball games played to earn a paycheck. (16) definition also means abandonment of the traditional usage in which"sport,"derived (17) Middle English disporter,refers to any light hearted recreational activity.In the. (18) of some 18th- century aristocrats,a game of backgammon and the seduction of (19) milkmaid were both considered good sport,but this usage of the term (20) become archaic.

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