h=v0t+0.5at^2100=2v0+20v0=40vt=v0+at =40+10*2 =60vt=at60=10tt=6h=0.5gt^2 =0.5*10*36 =180
h＝1/2 g t^2,(h-100)=1/2 g (t-2)^2。二式连列可解得t=6s,h=180m.v=gt,v=60m/s
