Questions for Thermodynamics (3)

SCHOOL-LEVEL QUESTIONS

  1. Liquid X has a specific heat capacity Cx. It is mixed with an equal mass of liquid Y with specific heat capacity Cy. The temperature of X is initially greater than that of Y. What is the ratio of the temperature rise of  X over that of Y? Express this in terms of the two heat capacities.
  2. What is the average kinetic energy of water molecules at 120C?
  3. A bullet is fired into an iron plate, where it deforms and finally stops. As a result, the temperature of the bullet increases by an amount dT1. A bullet having twice the mass and half the speed causes the temperature change dT2. What is the ratio dT2/dT1 ?
  4. A block of metal at 90C is placed in a beaker of water of the same mass at 0C. The final temperature of the water and block are 9C. Assuming that this system is isolated from its surroundings, what is the ratio of the specific heat of the water to the specific heat of the metal?
  5. The kinetic energy of gas A with molar mass 3, at temperature T, is K. The kinetic energy of gas B with molar mass 5, at temperature T, is k. What is the ratio K/k ?
  6. As altitude increases, does the latent heat of vaporisation of a gas increase or decrease?

HEAT ENGINES AND ENTROPY

  1. During each cycle, a heat engine absorbs 400J from a high-temperature reservoir and discards 350J into its low-temperature reservoir. What is its efficiency?
  2. An engine of efficiency 25% discards 75J of heat into its low-temperature reservoir in every cycle. How much heat does it absorb per cycle?
  3. A carnot cycle operates between the temperatures of 500K and 300K. If it absorbs 10J of heat at the start of every cycle, how much heat does it discard at the end?
  4. A refrigerator is left with its door open in an insulated room. At the end of 24hrs, how has the temperature and entropy of the room in total changed?
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