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问题 问答题

要求摩托车由静止开始在尽量短的时间内走完一段直道，然后驶入一段半圆形的弯道，但在弯道上行驶时车速不能太快，以免因离心作用而偏出车道．求摩托车在直道上行驶所用的最短时间．有关数据见表格．（提示：可用图象法解）

启动加速度a14m/s2
制动加速度a26m/s2
直道最大速度v140m/s
弯道最大速度v218m/s
直道长度s243m

答案

设最大速度为Vm，则

S=

vm2
2a1
+
v22-vm2
2a2

代入数据243=

vm2
2×4
+
182-vm2
-2×6

解得vm=36m/s，

所以加速时间为t1=

vm
a1
=
36
4
s=9s

减速时间为：t2=

v2-vm
a2
=
18-36
-6
s=3s

所以在直道上运动的最短时间是t=t1+t2=9s+3s=12s

答：摩托车在直道上行驶所用的最短时间是12s．

单项选择题

Visitors to this country are normally admitted for six months, but foreign students can usually stay for one year. They must (51) an educational institution, and they are required to study for a minimum of fifteen hours a week on a (52) course. Prospective students have to show that they can afford their studies, and that they have sufficient (53) resources to support themselves (54) in this country.

In order to work here the foreigner needs a work permit, (55) must be applied for by his prospective employer. The problem here is that the Department of Employment has the right to grant or (56) these permits, and there is little that can be done (57) it; it would be extremely unwise for a foreign visitor to work (58) a permit, since anyone doing so is liable to immediate deportation (驱逐出境). There are some people from the Common Market countries, who are often given (59) residence permits of up to five years. Some other people, such as doctors, foreign journalists, authors and others can work without permits, and foreign students are normally allowed to (60) part-time jobs while they are studying here.

56().

A.solve 

B.refuse 

C.sell 

D.buy
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下列各项属于《期货交易所管理办法》管辖范围的是（）。

A．上海期货交易所

B．香港期货交易所

C．芝加哥期货交易所

D．澳洲雪梨期货交易所
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