问题 计算题

(14分)如图,竖直放置的足够长的光滑平行金属导轨MN、PQ,有一垂直穿过导轨平面的匀强磁场,导轨上端M与P间拉一阻值R=0.40Ω的电阻,质量为0.01Kg、电阻为r=0.30Ω的金属棒ab紧贴导轨自由下滑,其下滑距离与时间的关系如下表,导轨电阻不计。(g=10m/s2

时间t(s)00.10.20.30.40.50.60.7
下滑距离s(m)00.10.30.71.42.12.83.5
(1).当t=0.7S时,重力对金属棒做功的功率

(2)金属棒在0.7S内,电阻R上产生的热量

(3)从开始运动到0.4S的时间内,通过金属棒的电荷量

答案

(1)P=0.7W  (2)QR=0.06J  (3)q=0.2C

题目分析:(1)当t=7S时,速度(1分)

重力的功率P=mgv  (1分) 得P="0.7W" (1分)

(2)当t=7S时,下落高度为h1,电路中总热量为Q

根据功能关系(2分)得Q="0.105J" (1分)

电阻R产生的热量(2分)得QR=0.06J(1分)

(3)当t=4S时,下落高度为h2,导轨宽L,磁感应强度B

 (2分)

当t=7S时,已匀速(2分)得q=0.2C (1分)

点评:学生要清楚金属棒是先做加速直线运动,再做匀速直线运动,能熟练运用速度的定义式,功率的公式,功能关系,电荷量的公式,安培力公式解相关问题。

问答题 简答题
单项选择题

The Republican Party has lost its mind. To win elections, a party needs votes, obviously, and constituencies. First, however, it needs ideas. In 1994--95, the Republican Party had after long struggle advanced a coherent, compelling set of political ideas expressed in a specific legislative agenda. The political story of 1996 is that this same party, within the space of six weeks, then became totally, shockingly intellectually deranged.

Then, astonishingly, on the very moment of their philosophical victory, just as the Republicans prepared to carry these ideas into battle in November, came cannon fire from the rear. Pat Buchanan first came out to declare a general insurrection. The enemy, according to Buchanan, is not the welfare state. It is that conservative icon, capitalism, with its ruthless captains of industry, greedy financiers and political elites (Republicans included, of course). All three groups collaborate to let foreigners--immigrants, traders, parasitic foreign-aid loafers--destroy the good life of the ordinary American worker.

Buchananism would support and wield a big and mighty government apparatus to protect the little guy from buffeting, a government that builds trade walls and immigrant-repelling fences, that imposes punitive taxes on imports, and that polices the hiring and firing practices of business with the arrogance of the most zealous forcer.

Republicans have focused too much on the mere tactical dangers posed by this assault. Yes, it gives ammunition to the Democrats. Yes, it puts the eventual nominee through a bruising campaign and delivers him tarnished and drained into the ring against Bill Clinton.

But the real danger is philosophical, not tactical. It is axioms, not just policies, that are under fire. The Republican idea of smaller government is being ground to dust--by Republicans. In the middle of an election year, when they should be honing their themes against Democratic liberalism, Buchanan’s rise is forcing a pointless rearguard battle against a philosophical corpse, the obsolete paleoconservatism--a mix of nativism, protectionism and isolationism--of the 1930s.

As the candidates’ debate in Arizona last week showed, the entire primary campaign will be fought on Buchanan’s grounds, fending off his Smoot-Hawley-Franco populism. And then what After the convention, what does the nominee do Try to resurrect the anti-welfare state themes of the historically successful ’94 congressional campaign

Political parties can survive bruising primary battles. They cannot survive ideological meltdown. Dole and Buchanan say they are fighting for the heart and soul of the Republican Party. Heart and soul, however, will get you nowhere when you’ve lost your way--and your mind.

The passage shows that the writer is ()the present situation.

A. surprised at

B. annoyed at

C. puzzled by

D. confused by