Question

How long does it take a 750-W coffeepot to bring to a boil 0.85L of water initially at 15?C?

Answer 1

Answer:

$t=5.176\ s$

Explanation:

power rating of the coffee pot, $P=750\ W$

volume of water to be boiled, $V=0.85\ L\ \Rightarrow mass,\ m=0.85\ kg$

initial temperature of water, $T_{i}=15^{\circ}C$

mass of aluminium in the pot, $m_a=0.36\ kg$

specific heat of aluminium, $c_a=900\ J.kg^{-1}.K^{-1}$

specific heat of water, $c_w=4186\ J.kg^{-1}.K^{-1}$

Considering that the water and aluminium are always at the same temperature.

Now the heat required to bring the water in the pot to 100°C:

$Q=(m_a.c_a+m.c_w)\Delta T$

$Q=0.36\times 900+0.85\times 4186$

$Q=3882.1\ J$

Therefore time required to boil the water:

$t=\frac{Q}{P}$

$t=\frac{3882.1}{750}$

$t=5.176\ s$