3. Sand casting [8 points] A sand mold has a downsprue of length = 15 cm. The cross-sectional area at the bottom of the sprue is 3.125 cm. The sprue leads into a horizontal runner which feeds the mold cavity, whose volume is 1172 cm. Determine: 3.1. the velocity of the molten metal flowing through the base of the downsprue, assuming that it is poured starting from a stationary state at the top of the downsprue, [4 points] 3.2. the volume rate of flow [2 points], and 3.3. the time required to fill the mold cavity, assuming continuity is preserved in the runner and gate system, and ignoring the time taken to fill runners and risers [2 points].