54) Ra value ( in micro meter) corresponding to roughness grade symbol N7 is

55) Calcute the turning time required to finish cut a mild steel rod of diameter 40mm for 100mm length in one pass, on a lathe with feed rate of 0.2mm/revolution and at a speed of 100 rpm?

56) What is the approximate radius of righ circular cylinder of height 100 mm which is cast from a cube of 100 mm size

57) What is the area of circle which passes through all the corners of a square of side 8 cm?

58) Following spindle speeds (in RPM) are available in a drilling machine - 100, 200, 400 and 800. For drilling Dia 20 mm hole in mild steel plate, at cutting speed 30 m/min, what is the preferred RPM to run the machine?