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
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