O点振动方程：y=-Asinwt，A=0.04m,w=2π/T，T=λ/U=0.04/0.02=2s-->w=π:y=-0.04sin(πt)=0.04cos(πt+π/2)波动方程：y=0.04cos(πt-kx+π/2)k=2π/λ=50π--->y=0.04cos(πt-50πx+π/2)
