材料热力学习题答案1

The problems of the first law 1. a lead bullet is fired at a frigid surface. At what speed must it travel to melt on impact, if its initial temperature is 25℃ and heating of the rigid surface of the rigid surface is neglected? The melting point of lead is 327℃. The molar heat of fusion of the lead is 4.8kJ/mol. The molar heat capacity CP of lead may be taken as 29.3J/(mol K) (1.1) Solution: )/(5.112.20721]108.4)25327(3.29[2121)(2322smVvnnWQnMvmvWHTCnQQQabsorbmeltingpmeltincreaseabsorb 2. what is the average power production in watts of a person who burns 2500 kcal of food in a day? Estimate the average additional powder production of 75Kg man who is climbing a mountain at eh rate of 20 m/min (1.2) Solution)/(24560208.975)/(12160602410467000//)(104670001868.4102500sin3SJthmgPSJtQtWPJQgincreaBurningBurning 3 One cubic decimeter (1 dm3) of water is broken into droplets having a diameter of one micrometer (1 um) at 20℃. (1.3) (a) what is the total area of the droplets? (b) Calculate the minimum work required to produce the droplets. Assume that the droplets are rest (have zero velocity) Water have a surface tension of 72.75 dyn/cm at 20℃ (NOTES: the term surface energy (ene/cm2) is also used for surface tension dyn/cm) Solution )(25.218)106103(1075.72)(103)101(4)101(34)101(232523263631JSWmnSSSingletotal 4.Gaseous helium is to be used to quench a hot piece of metal. The helium is in storage in an insulated tank with a volume of 50 L and a temperature of 25℃, the pressure is 10 atm. Assume that helium is an ideal gas. (a) when the valve is opened and the gas escapes into the quench chamber (pre...