BC 由题图乙可以知道质点A在该时刻的振动方向是沿y轴正方向,则说明波沿x轴负方向传播,所以A是错误的;这列波的波速是25m/s,所以B是正确的;经过Δt=0.4s即经过半个周期,在半个周期内A质点通过的路程是4m,所以C是正确的;由于波沿x轴负方向传播,P质点将向下振动,质点P将比质点Q后回到平衡位置,所以D是错误的.
The year was 1932. Amelia Earhart was flying alone from North America to England in a small single—engined aeroplane. At midnight, several hours after she had left Newfoundland, she ran into bad w