发达国家一般通过()吸引优秀学生学习。当他们获得学位之后就实施就业优惠和移民政策留住人才。
A.丰厚的奖学金
B.优秀的师资队伍
C.高端的科研设备
D.浓厚的学习氛围
参考答案:A
Read and choose.
( )1. What's the matter?
( )2. How tall are you?
( )3. How heavy is your sister?
( )4. How do you get to the zoo?
( )5. Who is taller?
A. She's 50 kg.
B. 170 cm.
C. My brother is taller than me.
D. I have a fever.
E. By car.
某宇航员在太空站内做了如下实验:选取两个质量分别为mA=0.1kg、mB=0.2kg的小球A、B和一根轻质短弹簧,弹簧的一端与小球A粘连,另一端与小球B接触而不粘连.现使小球A和B之间夹着被压缩的轻质弹簧,处于锁定状态,一起以速度V0=0.1m/s做匀速直线运动,如图所示,过一段时间,突然解除锁定(解除锁定没有机械能损失),两球仍沿原直线运动,从弹簧与小球B刚刚分离开始计时,经时间t=3.0s,两球之间的距离增加了S=2.7m,求弹簧被锁定时的弹性势能Ep?