Question

Number 29 plz help physics

Answer 1

a. E = 900000 J = 900 KJ

b. ΔT = 8.18 °C

c. Cost = $ 7.2

Step-by-step explanation:

a.

The energy can be given by:

`E = Pt`

where,

E = Energy = ?

P = Power = 500 W

t = time = (0.5 h)(3600 s/1 h) = 1800 s

Therefore,

`E = (500\ W)(1800\ s)`

E = 900000 J = 900 KJ

b.

The change in temperature of room air is given by the following formula:

`0.5E = mC\Delta T\\` (since 50% of energy is used to heat air)

where,

m = mass of air = 50 kg

C = specific heat of air = 1.1 KJ/kg.°C

ΔT = Change in temperature of air = ?

Therefore,

`(0.5)(900\ KJ) = (50\ kg)(1.1\ KJ/Kg.^oC)\Delta T`

ΔT = 8.18 °C

c.

First, we will calculate the total energy consumed:

`E = (0.5\ KW)(6\ h/d)(30\ d)\\E = 90\ KWh`

Now, for the cost:

`Cost = (Unit\ Cost)(Energy)\\Cost = (\$ 0.08\KWh)(90\ KWh)`

Cost = $ 7.2