91影视

A premature baby in an incubator can be dangerously cooled even when the air temperature in the incubator is warm. Explain.

(II)Determine the energy content of 100 g of Karen鈥檚 fudge cookies from the following measurements. A 10-g sample of a cookie is allowed to dry before putting it in a bomb calorimeter (page 396). The aluminum bomb has a mass of 0.615 kg and is placed in 2.00 kg of water contained in an aluminum calorimeter cup of mass 0.524 kg. The initial temperature of the system is 15.0掳C, and its temperature after ignition is 36.0掳C.

Question:Heat loss occurs through windows by the following processes: (1) through the glass panes; (2) through the frame, particularly if it is metal; (3) ventilation around edges; and (4) radiation.

(a) For the first three, what is (are) the mechanism(s): conduction, convection, or radiation?

(b) Heavy curtains reduce which of these heat losses? Explain in detail.

(I)How much heat is needed to melt 23.50 kg of silver that is initially at 25掳C?

A piece of wood lying in the Sun absorbs more heat than a piece of shiny metal. Yet the metal feels hotter than the wood when you pick it up. Explain.

(II)During exercise, a person may give off 185 kcal of heat in 25 min by evaporation of water (at 20掳C) from the skin. How much water has been lost? [Hint: See page 399.]

The Earth cools off at night much more quickly when the weather is clear than when cloudy. Why?

(II) What mass of steam at 100掳C must be added to 1.00 kg of ice at 0掳C to yield liquid water at 30掳C?

An 鈥渆mergency blanket鈥� is a thin shiny (metal-coated) plastic foil. Explain how it can help to keep an immobile person warm.

(II) A 28-g ice cube at its melting point is dropped into an insulated container of liquid nitrogen. How much nitrogen evaporates if it is at its boiling point of 77 K and has a latent heat of vaporization of 200 kJ/kg? Assume for simplicity that the specific heat of ice is a constant and is equal to its value near its melting point.