82 Chapter 4 • Heat
7. It is required to raise the temperature of 50 kg of water from15 °C to 90 °C. Determine the amount of heat energy that the water will absorb if the specific heat capacity of the water can be taken as 4,2 kJ/kg °C.
(15,75 MJ)
8. Calculate the heat energy required to heat a 30 kg piece ofmetal from30 °C to 350 °C. Take the specific heat capacity of themetal as 395 J/kg °C.
9. Themass of a steel component is 12,5 kg. Calculate the amount of heat energy required to change its temperature from50 °C to 500 °C if the heat capacity of the steel is 0,486 kJ/kg °C.
10. Calculate the heat required to heat 30 kg of steel from20 °C to 180 °C if the specific heat capacity of the steel is 486 J/kg °C.
12. Determine the temperature change that will take place if 234 kJ of heat energy is applied to a 5 kg copper ball. Take the specific heat capacity of copper as 390 J/kg °C.
11. Calculate the amount of heat energy required to heat 500 g of water through 60 °C if it has a specific heat capacity of 4,2 kJ/kg °C.
(3,792 MJ) (2,734 MJ) (2,333 MJ) (126 kJ) (120 °C)
13. Calculate the amount of water that can be brought from20 °C to a boiling point of 100°C by the addition of 1,5 MJ of heat energy. Take the specific heat capacity of the water as 4 200 J/kg °C.
14. Determine themass of copper that can be heated through 150 °C by 2 MJ of heat energy. Assume that no heat is lost and that the specific heat capacity of copper is 0,39 kJ/kg °C.
15. Determine the amount of heat energy required to boil 2,5 kg pure water at sea level if the initial temperature of the water is 20 °C. The specific heat capacity of the watermay be taken as 4,2 kJ/kg °C.
(4,464 kg) (34,19 kg) (840 kJ)
16. Calculate the amount of heat energy required to raise the temperature of 5 kg of steel from25 °C to 275 °C if the specific heat capacity of the steel is 495 J/kg °C.
17. A brass casting with amass of 4 kg absorbs 100 kJ of heat energy. If the initial temperature of the casting was 15 °C and the specific heat capacity 370 J/kg °C, determine the final temperature of the casting.
Exercise 4.4
1. Consider a hot copper ball being dropped into a container with cold water and assume that no heat is lost. 1.1 What will happen between the two substances? 1.2 What type of transfer will take place? 1.3 What will ultimately result?
(618,75 kJ) (82,57 °C)
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