唔識計heat.....................

Energy given out by the kettle:

E = Pt

E = P ( 10 )( 60 ) = 600P

The energy required to raise the temperature of water from 30*C to 100*C:

E1 = m( 4200 )( 100 - 30 ) = 294000m

As given,

E = E1

600P = 294000m

P = 490m

The energy required to vapourize half of the boiling water:

E2 = ( m / 2 )( 2.268 x 10^6 )

Then,

Pt = ( m / 2 )( 2.268 x 10^6 )

490mt = ( m / 2 )( 2.268 x 10^6 )

t = 38.6 min ( cor. to 3 s.f. )

Hence the extra time required is 38.6 min.