Gravitation

A projectile is thrown straight upward from the earth's surface with an initial speed \(v=\alpha v_e\) where \(\alpha\) is a constant and \(v_e\) is the escape speed. The projectile travels upto a height 800 km from earth's surface, before it comes to rest. The value of the constant \(\alpha\) is (radius of the earth \(=6400 \mathrm{~km}\))