Y/X=tanθ{(1/2)gt^2}/(Vo*t)=tanθ解出,t=(2√3)Vo/(3g)Y=(1/2)gt^2=(Vo^2)*(2/3g)=(2Ek/m)*(2/3g)动能定理:mgY=Ek'-EkEk'=Ek+mgY=Ek+(4/3)*Ek=7Ek/3=14J
14J