Through holes of $$10$$ $$mm$$ diameter are to be drilled in steel plate of $$20$$ $$mm$$ thickness. Drill spindle speed is $$300$$ $$rpm,$$ feed $$0.2$$ $$mm/rev$$ and drill point angle is $${120^0}.$$ Assuming drill over travel of $$2mm$$ the time for producing a hole will be

The time taken to drill a hole though a $$25$$ $$mm$$ thick plate with the drill rotating at $$300$$ $$rpm$$ and moving at a feed rate of $$0.25$$ $$mm$$/revolution is

The abrasive material used in grinding wheel selected for grinding of ferrous alloys is