The block leaves the surface when the normal force becomes zero, which occurs when the centripetal force equals the component of gravity, mv²/R = mgcosθ. The velocity is given by v²=2gh. Also, from the geometry, cosθ = (R-h)/R. Equating these gives (R-h)/R = 2h/R, which simplifies to R - h = 2h, so 3h = R, and h = R/3. [cite: 56, 57, 62, 63]