11. the optimum shape of a riser is spherical to ensure that it cools more slowly than the casting it feeds. spherically shaped risers, however, are difficult to cast. (1) sketch the shape of a blind riser that is easy to mold, but also has the smallest possible surface area-to-volume ratio. (2)compare the solidificationtime of the riser in part (a) to that of a riser shaped like a right circular cylinder. assumethat the volume of each riser is the same, and that for each the height is equal to the diameter.