20. Heat and Temperature

(II) High-altitude mountain climbers do not eat snow, but always melt it first with a stove. To see why, calculate the energy absorbed from your body if you

(a) eat 1.0 kg of -15°C snow which your body warms to body temperature of 37°C;

(I) How much heat is needed to melt 26.50 kg of silver that is initially at 25°C?

(I) If 3.40 x 10⁵ J of energy is supplied to a container of liquid oxygen at -183° C , how much oxygen can evaporate?

(II) At a crime scene, the forensic investigator notes that the 6.2-g lead bullet that was stopped in a doorframe apparently melted completely on impact. Assuming the bullet was shot at room temperature (20°C), what does the investigator calculate as the minimum muzzle velocity of the gun?

"(II) An iron boiler of mass 180 kg contains 710 kg of water at 18°C. A heater supplies energy at the rate of 58,000 kJ/h. How long does it take for the water

(a) to reach the boiling point, and "

(II) During exercise, a person may give off 185 kcal of heat in 25 min by evaporation of water (at 20°C) from the skin. How much water has been lost? [Hint: See page 548.]

An iron meteorite melts when it enters the Earth’s atmosphere. If its initial temperature was -105° C outside of Earth’s atmosphere, calculate the minimum velocity the meteorite must have had before it entered Earth’s atmosphere.

(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.