Unit 43: Heat Exchange
Practice Problems
Note: problem difficulty is ranked using a star system.
(*) One-star problems are fundamental to the unit, and can be done relatively quickly. Use these problems to introduce yourself to the material.
(**) Two-star problems are more difficult, and require an understanding of one or two key concepts. Use these problems to test your understanding of the material.
(***) Three-star problems are the most difficult, and require some creative thinking in addition to a deep familiarity with multiple key concepts. Use these problems to challenge yourself; if you can complete one of these, you’re on your way to mastering the material.
**Q43.2) 5kg of 0°C ice is mixed with 5kg of 10°C water in an insulated container. How much ice remains once the system reaches thermal equilibrum?
**Q43.1) A 20kg rock initially at 300°C is placed in a bathtub filled with 400kg of 23°C water. What will be the equilibrium temperature of the system? Assume the specific heat capacity of the rock is 2500 J/kg/°C.
***Q43.3) How many times would you have to slap a thawed turkey to fully cook it? You may assume the following things:
the turkey starts at room temperature (20°C) and needs to reach 74°C to be considered fully cooked,
the turkey has a mass of 4kg,
the specific heat capacity of turkey meat is 3060 J/kg/°C,
your hand has a mass of 406g,
the average impact speed of your hand on the turkey is 9m/s,
20% of the kinetic energy of each slap is transferred to the turkey as heat.