You have been given an aluminium block in which hole is to be drilled. From the tool manufacturer's cutting speed chart, 77 m/min speed to be used for aluminium. The r.p.m to be used for 10 mm drill bit is

39) The approximate depth of thread for M8 x 1 is

40) General formula for the length of the snap-head rivet is (t - thickness of the joint to be riveted and d - diameter of the rivet)

41) Derivative of -sinx with respect to x is

42) Perimeter of the semicircle having diameter 'd' is