# Physics

An Electricity account shows that a household has used 1400 units of electrical energy during a three month period. Calculate :
a)the number of joules of energy used in this time.
b)the average number of joulesof energy used perday .
c)the average power consumption in watts.
d)the cost of electricity in this three month period if each unit costs \$2.50.

Help ! :(

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1. Power companies normally measure energy
in Kil0Watt hours(kWh). So we'll assume
1400 units = 1400 kWh.

a. Energy = 1400kwh * 3.6*10^6J/kwh =
5040*10^6 = 5.04*10^9 Joules.

b. Energy = 5040*10^6J / 90days = 56*10^6 = 5.6*10^7 Joules/day.

c. t = 90days * 24h/day = 2160 hours.
P = 1400kwh * 1000w/kw * (1/2160h) =
648.1 Watts used.

d. 1400kwh * \$2.50/kwh = \$3500.

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