0.5克的25℃水用4分鐘沸至70℃,若要升至100℃,需要多久?

Assume no energy is lost to the surroundings,
suppose the power of the heater is P .
By E = Pt and E = mcΔT,
Pt = mcΔT
P(4)(60) = (0.5)(4200)(70-25)
P = 393.75W
Then,
(393.75)( t ) = (0.5)(4200)(100-25)
t = 400s
= 6 min 40s which is the required time