Problem

A kettle with 2 litre water at

27^\circ\text{C}

is heated by operating coil heater of power 1 kW. The heat is lost to the atmosphere at constant rate

160 \text{ J/s}

, when its lid is open. In how much time will water heated to

77^\circ\text{C}

with the lid open? (specific heat of water =

4.2 \text{ kJ}/^\circ\text{C}\cdot\text{kg}

) a. 8 min 20 s b. 6 min 2 s c. 14 min d. 7 min