Question

How long will it take a 50 watts heater to melt 100 g of ice at 0 C

Answer 1

Solution. Using the formula that relates heat energy to mass and heat of fusion:

$$q=m \Delta H_f$$

where q is heat energy; m=100g is mass; ∆H_f= 334 J/g is heat of fusion for ice. On the other hand, the heat generated by the heater is equal to

$$q=Pt$$

where P=50 watts is power; t is time. Since the energies are equal, we obtain

$$m \Delta H_f=Pt$$

Therefore

$$t=\frac {m\Delta H_f}{P}=\frac{100\times 334}{50}=668s$$

Answer. 668 seconds