Problem Graphic


Ann is living in a dormitory room, and she has a small fan in the room. On a summer day, she turns on her fan before leaving for classes, to cool the room before she comes back in the evening. Does it work?

What is known:

  • The size of the room is 4 m x 6 m x 6 m
  • The power of the fan is 150 W
  • She leaves at 8:00 am and comes back at 6:00 pm
  • The room temperature is 15 oC when she leaves in the morning

  • What will the temperature of the room be when Ann comes back in the evening?

  • Consider the air in the room as a system
  • Use specific heat values at the average room temperature
  • All the energy from the fan becomes internal energy of the air in the room