What is the potential energy of the ball as it is half way through the fall, 20 meters high?

Ahypothetical metal has an orthorhombic unit cell for which the a, b, and c lattice parameters are 0.413 nm, 0.665 nm, and 0.876 nm, respectively. (a) if there are 8 atoms per unit cell and the atomic packing factor is 0.536, determine the atomic radius (in nm). (b) if the density is 3.99 g/cm3, calculate the metal's atomic weight (in g/mol).