A certain type of D-cell battery that costs $0.50 is capable of producing 1.3 V and a current of 0.3 A for a period of 75 hours. Determine the cost of the energy delivered by this battery per kilowatt hour. (For comparison, the approximate cost of energy purchased from electric utilities in the United States is $0.12 per kilowatt hour.)

$3.51

Explanation:

The energy (E) delivered by a system is the product of the power (P) dissipated by the system and the time (t) taken for the dissipation. i.e

E = P x t (i)

Where;

The power (P) is the product of the current (I) flowing through the system and the voltage (V) across the system. i.e

P = I x V

Substituting P = I x V into equation (i) gives;

E = (I x V) x t

=> E = IVt    (ii)

From the question;

Current (I) = 0.3A

Voltage (V) = 1.3V

time (t) = 75 hours = 75h

Substituting these values into equation (ii) gives;

=> E = 0.3 x 1.3 x 75

=> E = 29.25 Kwh

The energy delivered is 29.25Kwh

But in the U.S;

$0.12 = 1Kwh

=> 29.25Kwh = 29.25 x $0.12

=> $3.51

Therefore, the cost of the energy delivered by this battery per kilowatt hour is $3.51