Explain why is it difficult to burn a wet piece of wood.

47 Name three characteristics of a fuel that determines its quality. 48 The heat produced by burning of cow dung cake of mass 210 g raised the temperature of 50 g of water by 2° C. Assuming that all the heat was utilized for heating water whose specific heat capacity is 4.2 J/g ° C, calculate the calorific value of the dung cake. 50 Pouring dry sand over fire helps to contain it. Explain why? 51 What is the ultimate source of almost all our sources of energy?