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A kettle with 2 litre water at 27^@C is ...

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 s

B

6 min 2 s

C

14 min

D

7 min

Text Solution

Verified by Experts

The correct Answer is:
A
Net power available per second,
`P = 1000 - 160 = 840 J//s`
Heat required,
`Q = msDeltatheta = (2)(4200)(77-27)`
`=420000 J`
`:. `Time required `= Q/P = 500 s = 8 min 20s`.
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