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如图甲所示，质量mB=1kg的平板小车B在光滑水平面上以v1=1m/s的速度向左匀速运动．当t=0时，质量mA=2kg的小铁块A以v2=2m/s的速度水平向右滑上小车，A与小车间的动摩擦因数为μ=0.2．若A最终没有滑出小车，取水平向右为正方向，g=10m/s2，求：

（1）A在小车上相对小车停止运动时，小车的速度大小

（2）通过计算，在图乙所示的坐标纸中画出1.5s内小车B运动的速度一时间图象．

答案

（1）A在小车上停止运动时，A、B以共同速度运动，

设其速度为v，取水平向右为正方向，由动量守恒定律得：

mAv2-mBv1=（mA+mB）v，解得，v=lm/s；

（2）设小车做匀变速运动的加速度为a，时间t，

由牛顿运动定律得：μmAg=

m B
a，

由速度公式得：v=-v1+at，

解得：t=

v+v1
a
=0.5s，

则小车B先做匀减速运动，后做反向的匀加速运动，

最后做匀速直线运动，小车的速度时间图象如图所示．

答：（1）小车速度大小为1m/s；

（2）图象如图所示．

多项选择题

灭火剂按平时存在的形态可分为三类（）。

A、液体灭火器

B、气体灭火剂

C、固体灭火剂

D、其他灭火剂
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The Commission is expected to propose allowing people to choose which legal jurisdiction they would come under, based on their (1) or their residency. But the proposal is set to (2) because of the very different laws on divorce that apply across the EU. The Commission wants to (3) problems over which law to apply when, for example, a married couple from one member state is (4) in another member state or when the couple is of different EU nationalities.
The (5) of member states are said to be (6) the idea and responded positively to a (6) which followed the (8) of a Commission Green Paper. With 15 percent of German divorces each year involving couples of different nationalities, the government of Berlin (9) see resolved the issue of which laws should apply.
But some member states are expected to resist the (10) which would involve allowing different divorce laws to be applied in their countries. For example, in Ireland where the divorce law states a couple must have been separated for four years, establish that their marriage has broken down and be offered (11) , a couple from Sweden could apply to an Irish court to allow them to divorce under Swedish law, where divorce can be (12) quickly.
The Irish government’s (13) to the Commission on the Green Paper stated: "Ireland is not in favor of allowing (14) to choose the applicable law, as this could be open to abuse.., such abuse would be likely to (15) most on divorce regimes, such as that of Ireland, which require a relatively long separation period." Ireland, like the UK, however, is allowed to choose whether to "opt-in" to such a proposal under rules agreed in the Amsterdam treaty. Malta has no such (16) but could (17) the proposal in the Council of Ministers since (18) approval will be required.
"It is going to lead to (19) ," said Geoffrey Shannon, Irish expert on the Commission on European Family Law, which examines the (20) of EU family law.
The proposal would also mean that judges would have to be trained in the divorce law of all 25 member states.
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