Answer:
96 s.
Explanation:
(a)
From the question,
Q = cm(t₂-t₁)................... Equation 1
Where Q = heat required to boil the water, c = specific heat capacity of the water, m = mass of the water, t₂ = final temperature of water, t₁ = initial temperature of water
Note: The boiling point of water = 100 °C
Given: c = 4200 J/kg.°C, t₂ = 100 °C, t₁ = 20 °C
mass of water = density×volume
m = D×v, Where D = 1000 kg/m³, v = 1.00 L = 0.001 m³
Hence, m = 1000×0.001 = 1 kg.
Substitute into equation 1
Q = 4200×1(100-20)
Q = 4200×8
Q = 33600 J.
But,
P = Q/t................... Equation 2
make t the subject of the equation
t = Q/P................. Equation 3
Where P = power, t = time
From the question,
70 % of the available energy is absorbed by water.
P = 0.7×500 = 350 W.
Substitute into equation 2
t = 33600/350
t = 96 s.
