机械波的表达式为y=0.01cos(4t+0.4x) m,则()
A. 振幅为0.1m
B. 波速为10 m/s
C. 周期为π/3 s
D. 波沿x 轴正方向传播
查看答案
物体A的质量是B的2倍且静止,物体B以一定的动能E与A碰撞后粘在一块并以共同的速度运动, 碰撞后两物体的总动能为()
A. E
B. E/2
C. E/3
D. 2E/3
Your pen writes___. Where did you buy it?
A. good
B. nice
C. neat
D. well
He has lived and worked in China___1996.
A. in
B. since
C. for
D. by
You will be able to get good marks ____
A. while you are doing your homework by yourself
B. if you do some revision every day
C. before you begin to study hard
D. until you follow your teachers’ advice
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