CHAPTER 11 HEAT CHAPTER 11 EXERCISE 11A CONTINUED H
15. It has been proposed that drinking ice-cold water at 0 °C can help people of lose weight because the body uses stored energy in the form of fat to warm the water up to body temperature of 37 °C. (0.5 kg of fat stores about 1.6 × 108 J of energy.)
(i) Calculate the mass of ice-cold water that a person would need to drink in order to lose 0.5 kg of fat.
(ii) Give a reason why it would not be practical to drink ice-cold water in order to lose signifi cant weight.
16. 50 g of iro n at 120 °C is added to a 100 g copper calorimeter containing 120 g water at 25 °C. Assuming that the calorimeter is at the same temperature as the water and that there are no external heat losses, calculate the fi nal temperature of the water (SHC of iron = 450).
CHAPTER 11 EXERCISE 11B
1. How much energy is incident in one hour on a solar heating panel of 10 m2 if the solar constant is 1.35 kW m−2?
2. Describe how a heat pump operates, making reference to changes of state.
3. Explain why leaving a fridge door open does not cool the room it is in.
4. Explain how perspiring reduces temperature in an athlete.
5. What type of U-value material should builders use in insulating between house walls?
6. Explain how heat travels in: (i) solids
(ii) liquids (iii) gases.
7. How can you reduce the U-value of the walls of a house?
8. Why is the solar collector on solar panels painted black?
9. Why are heating elements that act as immersion heaters best placed at the bottom of the tank?
