A block of wood (dimensions : 40 ~cm 20 ~cm 10 ~cm ) is kept on a tabletop in three different positions: (a) with its side of dimensions 20 ~cm 10 ~cm ; (b) with its side of dimensions 10 ~cm 40 ~cm ; and (c) with its side of dimensions 40 ~cm 20 ~cm . The pressure exerted by the wooden block on the tabletop in these positions is represented by P_A, P_B and P_C , respectively. The pressure follows the trend