3. A metal object at 120°F is set on an insulating pad to cool. The temperature falls from 120°F to 100°F in 12 minutes. The surroundings are 65°F. Find the time required for that object to continue to cool from 98°F to 80°F. Assume negligible conduction and radiation losses in both cases.

19. The following fission reaction (shown below) occurs in a nuclear power plant. There are 1.50 x 1016 uranium-235 atoms that are simultaneously undergoing this reaction. The uranium is surrounded by 17.5 kg of heavy water, which has a specific heat capacity of 4.70 x 10³ J/kg °C. If 90% of the energy released in the nuclear reactions is absorbed as thermal energy by the heavy water, determine the increase in temperature of he heavy water. ✔✔✔✔ 235U+n→ Zr + 139 Te + 3(n) 92 40 52 mzr-94 = 93.906 u MTe-139 = 138.935 u Mu-235 = 235.044 u

1. An expensive vacuum system can achieve a pressure as low as 1.83 ✕ 10−7 N/m2 at 26°C. How many atoms are there in a cubic centimeter at this pressure and temperature? 2. The number of kilocalories in food is determined by calorimetry techniques in which the food is burned and the amount of heat transfer is measured. How many kilocalories per gram are there in a 4.80 g peanut if the energy from burning it is transferred to 0.600 kg of water held in a 0.130 kg aluminum cup, causing a 44.0°C temperature increase?

Q12. (a) Name any four types of radiation emitted by the sun? (b) A solar hot water system receives solar energy at the rate of 10.5 MJm2 per day. The efficiency of the solar collector is 0.8 and it has an area of 6.0 m2. The collector contains 0.250 m3 volume of water and the density of water is assumed to be 1000 kgm 3. The specific heat capacity of water C 4200 J/Kg. C. (i) Calculate the mass of water? (ii) Estimate the temperature rise of the water in the tank during the day.

2. Compare the heat loss from an insulated and an uninsulated copper pipe (k-400 W/m K) under the following conditions. The pipe has an internal diameter of 10 cm and an external diameter of 12 cm. The inside surface temperature of the pipe is at 110°C. The pipe is located in a space where all possible outside surface temperature of material was maintained at 30°C. The insulation available to reduce heat losses is 5 cm thick and its conductivity is 0.20 W/m K. If the furnace for heating the fluid in the pipe operating at an efficiency of 85% using natural gas priced at Cg = Php 1.00/MJ, what is the daily cost of heat loss per meter of pipe?