Question

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)`
A. `8 min 20 sec`
B. `6 min 2 sec`
C. `7 min`
D. `14 min`

Answer 1

Correct Answer - A
Net `= (Q)/(t) = 100 - 160`
`(ms Delta T)/(t) = 840`.