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本题为置换题实验班学生答题A题，其他班学生答B题．

A、飞机离地面高H=500m，水平飞行速度为v1=100m/s，追击一辆速度为v2=20m/s同向行驶的汽车，欲使投弹击中汽车，飞机应在距汽车水平距离多远处投弹？（g取10m/s2）

B、在高为20m的阳台上，用20m/s的初速度水平抛出一物体，不计空气阻力，g取10m/s2．求：（1）物体在空中运动的时间；（2）落地点与抛出点的水平距离．

答案

（1）炸弹做的是平抛运动，在竖直方向上做自由落体运动：

由h=

1
2
gt2可知，t=
2h
g
=10s

在水平方向上匀速直线运动：水平方向运动时间和飞行时间相同；

则s=v0t=10s×100m/s=1000m；

在此段时间内汽车向前行驶的距离s0=10s×20m/s=200m；

故s1=s-s0=1000m-200m=800m；

（2）根据h=

1
2
gt2可知，t=
2h
g
=2s

x=v0t=20×2m=40m

答：A、飞机应在距汽车水平距离800m处投弹；B、（1）物体在空中运动的时间为2s；（2）落地点与抛出点的水平距离为40m．

单项选择题

Mr. Brown was going away for a week. Before he left, he said to his son, "If anyone asks for me, you can tell him that your father has been out for doing something, and will be back in a week, then be sure to ask him to sit down for a cup of tea. "

"OK, Dad," said his son. But he was afraid his son couldn’t remember this, so he wrote these words down on a piece of paper and gave it to him. His son put it into his small pocket, took it out. and looked at it every now and then.

Four days passed, ’but no one came to see his father. The boy thought that there was no man to come and that the piece of paper was of no more use for him, so he burnt it that evening.

The next afternoon, someone knocked at the door. The boy opened it. A man was standing at the door and said, "Where is your father" The boy put his hand into his pocket at once and looked for the piece of paper. He could not find it. He suddenly remembered he had burnt it, so he shouted, "No more. "

The man was very surprised. He asked, "No more I met your father last week. When did it happen"

"Burnt yesterday evening.

What was burnt（）

A．The piece of paper.

B．Mr. Smith.

C．The visitor.

D．The boy.
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多项选择题

起重指挥人员，遵守安全措施（）

A.必须明确指挥人且佩戴明显的标志

B.起重指挥人员按照规定的指挥信号进行指挥

C.起重指挥人员吊装过程中发现问题要可以及随时调整吊装方案

D.吊装作业前先进行试吊，确认一切正常才能指挥吊车进行吊装作业
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