高一物理圆周运动题，急！

1, mgtanα=mV^2/r V=√(grtanα) 2, mgtanα+F=m4V^2/r F=m4V^2/r-mgtanα =4m(grtanα/r)-mgtanα =3mgtanα 3, mgtanα=mV^2/4r+F F=3mgtanα/4