30) A bar of length L meters extends by l mm under a tensile force of P. The strain produced in the bar is

31) A piece of wood having weight 5 kg floats in water with 60% of its volume under the liquid. The specific gravity of wood is

32) The unit of radio-activity is

33) In an application, the bearing is subjected to radial as well as axial loads. Which type of rolling contact bearings you would suggest?

34) Solder used for welding electrical wires is an alloly consisting of