①∵1mm=0.001m，∴1020mm=1020×0.001m=1.02m；②∵1s= 1 3600 h，∴1800s=1800× 1 3600 h=0.5h；③∵1km/h= 1 3.6 m/s，∴54km/h=54× 1 3.6 m/s=15m/s．故答案为：1.02；0.5；15．
