A kettle with $2\, littre$ water at $27\,^oC$ is heated by operating coil heater of power $1\, kW$. The heat is lost to the atmosphere at constant rate $160\, J/sec$, when its lid is open. In how much time will water heated to $77\,^oC$. (specific heat of water $= 4.2\, kJ/kg$) with the lid open ?

  • A

    $8\, min$ $20\, sec$

  • B

    $6\, min$ $2\, sec$

  • C

    $14\, min$

  • D

    $7\, min$

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[Heat of combustion $=8 \times 10^{3} Jg ^{-1}$  Specific heat of water $=4.2 Jg ^{-1} \; { }^{\circ} C ^{-1}$ ]

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