31.Suppose a rocketship is receding from the earth at a speed of 2/10th the velocity of light. a light in the rocketship appears blue to the passenger on the ship. What colour would it appear to an observer on the earth ?

32.Endoscope, used by doctors for examining the inside of a patients stomach, works on the principle of :

33.The minimum length of a plane mirror in which a person can see himself full length should be :

34.In storms, the roofs of some houses are carried away.This is in accordance with :

35.Consider the following statements about a thermos flask : 1. It is a practical device in which the heat flowing into or out of the system by conduction, convection or radiation is reduced as much as possible2. It consists of a double walled glass vessel3. The heat transfer by convection is minimised by silvering the surfaces and the radiation is minimised by evacuating the space between the walls.