2-15 An ice chest is constructed of Styrofoam [k = 0.033 W/m · •C] with inside dimensions of 25 by 40 by 100 cm. The wall thickness is 5.0 cm. The outside of the chest is exposed to air at 25 C with h = 10 W/m2 •C. If the chest is completely filled with ice, calculate the time for the ice to completely melt. State your assumptions. The enthalpy of fusion for water is 330 kJ/kg.

Air is trapped in the piston in the cylinder. A spring is connected to the upper portion of the piston and returns the force upon compression by the F = -kx equation. k = 50,000 N/m and x is the distance traveled when the piston is compressed. The piston is located 10 cm above the bottom of the cylinder with a cross-sectional area of 0.01 m2 and an initial condition of 1 bar and 25°C. In this state, the spring does not apply force to the piston. At this time, the system was reversibly heated and the temperature rose to 100°C. (a) What happened was (b) What is the heat transferred?

An open cylinder of air has a radius of 38.0 cm and a height of 50.0 cm, as shown in figure (a). 50.0 cm The air pressure is 1.00 atm and the temperature is 13.5°C. A 25.0 kg piston is then lowered onto the cylinder, forming an airtight seal, as shown in figure (b). The air inside is compressed until the piston reaches equilibrium (mechanical and thermal), and at this point the piston is a height h; from the bottom of the cylinder. Lastly, a 27.5 kg dog steps onto the piston, and the air in the cylinder again compresses, as show in figure (c). After reaching equilibrium, the air inside is again at 13.5°C, and the height of the piston decreases a distance Ah as shown. (a) What is the distance Ah (in mm) that the piston moves when the dog is on it? mm (b) To what temperature (in °C) should the gas be warmed to raise the piston and the dog back to h;? °C