如图所示，沿x轴正方向传播的一列横波在某时刻的波形图为一正弦曲线，其波速为200m/s，下列说法正确的是（ ）
A．从图示时刻开始，质点b比质点a先到平衡位置
B．从图示时刻开始，经0.01s质点a通过的路程为0.1m
C．若该波传播中遇到宽约3m的障碍物能发生明显的衍射现象
D．若该波波源从O点沿x轴正向运动，则在x=2000m处接收到的波的频率小于50Hz
A、波沿x轴正方向传播，此时b质点振动方向向下，而a质点直接向下向平衡位置运动，则质点a比质点b先到平衡位置．故A错误．
B、由图λ=4m，则T=
=0.02sλ v
t=0.01s=
T，经0.01s质点a通过的路程为S=2A=0.1m．故B正确．1 2
C、λ=4m＞3m，能发生明显的衍射现象．故C正确．
D、若该波波源从O点沿x轴正向运动，则在x=2000m处接收到的波的频率升高，大于50Hz．故D错误．
故选C
用方框中所给的单词适当形式填空，使短文通顺、正确、连贯（每个单词限用一次）。
Some students complain(抱怨) that their parents say a lot to them, but never 小题4:______ to them. Some of them even say it 小题5: . “My parents don't allow(允许) me to play computer games, 小题6: other classmates are doing that”. Others say, when they're 小题7: phone calls to friends, their parents like to ask if they're speaking to a boy or a girl. These make them very 小题8: . Some students even decide(决定) to leave home. But they don't know running away may bring them some more problems. Show your parents you're growing up. Then they'll feel you're no 小题9:__________ a small child. 小题10: you follow(听从) the advice, you'll have a happy life and never think of running away. |