A body is projected from a point on ground making an angle of 60o with horizontal. If radius of curvature of its trajectory at the top most point is 10 m, then radius of curvature at the point of projection is

If u be the velocity of projection, α be the angle of projection and ρ be the radius of curvature at the highest point, then ucosα2ρ=g⇒ρ=u2cos2αgAt point A, u2ρ1=gcosα⇒gcosα⇒ρ1=u2g1cosα=ρcos2α.1cosα=ρcos3α∴ ρ1=10cos60o3m=80 m