问题 问答题

(1)如图甲中一体积为1.0×10-4m3的实心物体A悬挂在弹簧测力计下,弹簧测力计读数为2.8N,物体A的密度为______kg/m3(g取10N/kg).若把物体完全浸没在某种液体中时,弹簧测力计的读数变为1.8N(如图乙),物体在这种液体中受到的浮力是______N.

(2)现有水银(ρ=13.6×103kg/m3)、水(ρ=1.0×103kg/m3)、酒精(ρ=0.8×103kg/m3),把物体A(不改变形状)分别放人上述三种液体中(三种液体足够多),A会在其中的______中处于漂浮状态.

(3)如图是水、水银、酒精的质量一体积图象,其中______是水银的质量-体积图象.(选填“a”、“b”或“c”)

答案

(1)由G=mg=ρvg,得:ρ=

G
vg
=
2.8N
1.0×10-4m3×10N/kg
=2.8×103kg/m3

F=G-F=2.8N-1.8N=1N;

(2)因为ρ水银>ρ,所以该物体在水银中漂浮.

(3)由图可知:相同体积的a、b、c三种物质,a的质量最大,即a的密度大,而密度最大的是水银,故应选a.

故答案为:2.8×103,1,水银,a.

单项选择题

Believe it or not,optical illusion can cut highway crashes.

Japan is a case in point.It has reduced automobile crashes on some roads by Rearly 75 percent using a simple optical illusion.Butst.ripes,called chevrons(人字形),painted on ther rads make drivers think that they are driving faster than they really are,and thus drivers slow down.

Now the American Automobile Association Foundation for Traffic Safety in Washington D.C. is planning t。repeat Japan’s success.Starting next year,the foundati。n will paint cheyrons and。ther pattems of stripes on selected roads around the country to test how well the patterns reduce highway erashes.

Excessive(too great)speed plays a major role in as much as one fifth of all fatal traffic accidents, according to the foundation.To help reduce those accidents,the foundation will conduct its tests in areas where speed-related hazards(danger)are the greatest curves,exit slopes,traffic circles,and bridges.

Some studies suggest that straight,horizontal bars painted across roads can initially cut the average speed of drivers in half.However,traffic。ften returns to full speed within months as driVers become used to seeing the painted bars.

Chevrons,scientists say,not only give drivers the impression that they are driving faster than they reallv are but als0 make a lane appear to be narrower.The result is a longer lasting reduction in highway speed and the number of traffic accidents.

The advantage of chevrons over straight, horizontal bars is that the former().

A. can keep drivers awake

B. can cut road accidents in half

C. will look more attractive

D. will have a longer effect on drivers

问答题 简答题