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THERMODYNAMICS - CASE STUDY

    Introduction


Bob's Bad Day
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Bob went home with a red print on his face yesterday. He was involved in a fight in school. Someone slapped his face which caused the temperature of the affected area of his face to rise. How fast the slapping hand is?

Known:

  • The mass of the slapping hand mhand = 1.5 kg
  • The mass of the affected tissue maffected tissue = 0.2 kg
  • The specific heat of the tissue c = 3.8 kJ/(kg-oC)
  • Temperature of face rise 1.5oC
    Questions


  Determine the velocity of the hand just before impact.

    Approach


System

 
  • Take the hand and the affected portion of the face as a system
  • The energy equation:

    Ein - Eout = ΔEsystem
                  = (ΔU + ΔKE + ΔPE)affected tissue +
                     (ΔU + ΔKE + ΔPE)hand