球下落1.8m所用的时间设为th=(1/2)gt^21.8=5*10t^2t=0.6s子弹击中球前运动时间T=t-0.5s=0.6s-0.5s=0.1sh=VT+(1/2)gT^21.8=0.1V+(1/2)*10*0.01=0.1V+0.05V=17.5m/s V太小！
初三物理
