问题 实验题

小明用如图所示的实验,探究影响浮力大小的因素。

(1)由图乙、丙可知,物体浸没在水中受到的浮力为         N;物体浸没在盐水中受到的浮力为       N。

(2)从图乙、丙可以看出浮力的大小与液体的            有关。

(3)小明利用图乙装置进一步探究:      

①当物体从接触液面到刚好完全浸没的过程中,发现弹簧测力计的示数是逐渐减小的,说明浮力大小与物体排开液体的        有关。

②当物体全部浸没在液体中后再继续下降的过程中,发现弹簧测力计示数保持不变,说明浮力的大小与物体浸没在液体中的深度        (选填“有关”或“无关”)

答案

(1)1  1.1 (2)密度 (3)①体积  ②无关

题目分析:可以用弹簧测力计的示数和物体的重力求浮力,即。由图乙、丙可知,物体浸没在水中受到的浮力为;物体浸没在盐水中受到的浮力为1.1N。从图乙、丙可以看出排开液体的体积相同,浮力的大小跟液体的密度有关。当物体从接触液面到刚好完全浸没的过程中,发现弹簧测力计的示数是逐渐减小的,说明浮力大小与物体排开液体的体积有关。当物体全部浸没在液体中后再继续下降的过程中,发现弹簧测力计示数保持不变,说明浮力的大小与物体浸没在液体中的深度无关。

点评:在此题中了解浮力的测量方法是解决此题的关键。浮力跟液体的密度和排开液体的体积有关。

单项选择题

Passage Two

Britain’s emissions of greenhouse gases, blamed by many scientists for contributing to global warming, have fallen by 14 percent since 1990, according to the latest government report.
British lakes and rivers are also on the road to recovery from acid rain poisoning, following successful curbs to air pollution from cars and heavy industry.
The report by the National Atmospheric Emissions Inventory (NAEI) attributed the drop in greenhouse gas emissions to several factors including: the introduction of catalytic converters on cars, a move toward low sulphur and lead-free petrol and a switch to gas from coal and oil in power generation.
Environment Minister Michael Meacher said the downward trend was welcome, but warned of complacency.
"Even though these figures are encouraging, we must not be complacent. There are still significant problems where we need to do more, for example, to further reduce greenhouse gases and harmful pollutants (污染物) such as ammonia and particulate matter," he said in a statement.
The government has a target to cut greenhouse gases by 23 percent by 2010 on 1990 levels. This is almost double the target of 12.5 percent to which the UK is committed under the Kyoto Protocol and there are signs that emissions are rising as generators return to using coal-fired power stations in the face of rising natural gas prices.
The Department of Environment Food and Rural Affairs (DEFRA) said substantial curbs on sulphur dioxide emissions across the UK and Europe had cut acid rain by half over the last 12 years. "Damaged freshwater lakes and streams are showing signs of recovery," it said.
But DEFRA warned of a new threat. "Nitrogen oxides and ammonia are the main air pollutants that must be tackled to stop future damage. "
The bulk of Britain’s ammonia emissions come from farm animal manure (粪肥), causing over-enrichment of land and waterways, said the report. Certain species rampage unchecked through this ultra-fertile environment, smothering the slower growing plants beneath them and choking streams and rivers. Nitrogen oxides enter the atmosphere from car exhausts and industry, creating health-damaging ozone and contributing to acid rain.

Which of the following has Britain NOT done to decrease emissions of greenhouse gases

A.Introduced catalytic converters on cars.

B.Encouraged use of low sulphur and lead-free petrol.

C.Replaced coal and oil with gas in power generation.

D.Closed down some heavy industry factories.

单项选择题