总距离是20米v铁=5200M/s v水=1500M/S V空=340M/S
T铁=s/v铁=20m/5200m/s=0.0038s
T水=s/v水=20m/1500m/s=0.0133s
T空=s/v空=20M/340m/s=0.0588s
T空-T铁=0.055s
总距离是20米v铁=5200M/s v水=1500M/S V空=340M/S
T铁=s/v铁=20m/5200m/s=0.0038s
T水=s/v水=20m/1500m/s=0.0133s
T空=s/v空=20M/340m/s=0.0588s
T空-T铁=0.055s