Bonjour,
1) Q = m x C(eau) x DeltaT
DeltaT = 28 - 10 = 18 degrés (C ou K)
m = Volume x p(eau)
==> Q = 630 x 1000 x 4180 x 18 = 4,74012.10^10 J
2) 1 kWh = 1000 Wh = 1000 x 3600 J = 3,6.10^6 J
==> Q = 4,74012.10^10 / 3,6.10^6 = 13167 kWh
Coût du chauffage = 13167 x 0,1 = 1316,7 €
3) Puissance = Energie/temps
==> P = Q/t
t = 48h = 48 x 3600s = 172800 s
==> P = 13167/172800 = 0,0762 kW