A rectangular block of steel C.S 100 x 150mm and 250mm height is to be cast without any riser. The block is moulded entirely in the drag of a green sand flask & is top gated. The scope of the flask is 200mm height & the height of the metal during pouring is 100mm above the cope level. A tapered sprue is employed & the gating ratio is 1:4:2. assume no energy losses in the system, The time taken (in seconds) to fill the fasting cavity, if the tapered sprues with 500mm2 exit area is used.