设听笛声处离山崖距离S鸣笛处离山崖距离S1则S+S1=V声t=340m/s*4s=1360m S-S1=V车t=20m/s*4s=80m解程组S=720mS1=640m即听笛声处离山崖720m鸣笛处离山崖640m
