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

Options

A. 5 min 40 s
B. 10 min 20 s
C. 8 min 20 s
D. 16 min 10 s

Answer

C

Explanation

Rate of heat gain =`1000-160=840J//s`
`therefore` Required time = `(2xx4.2xx10^(3)xx(77-27))/(840)=500s`
= 8 min 20 s