Question

The capacity of a storage battery, such as those used in automobile electrical systems, is rated in ampere-hours (A?h). A 50 A?h battery can supply a current of 50 A for 1.0 h, or 25 A for 2.0 h, and so on.

(I need some help on Part A & C Thank you : )

Part A

What total energy can be supplied by a 10V , 80A?h battery if its internal resistance is negligible?

Express your answer using two significant figures.

Part B

What volume (in liters) of gasoline has a total heat of combustion equal to the energy obtained in part (a)? (See Section 17.6; the density of gasoline is 900 kg/m3.)

Express your answer using two significant figures.

Ans: 7.0*10^-2

Part C

If a generator with an average electrical power output of 0.45kW is connected to the battery, how much time will be required for it to charge the battery fully?

Express your answer using two significant figures.

Answer 1

Part A

Total energy suuplied by battery = voltage x current x time

                                                        = 10 x 80 x 60 x 60

                                             = 2880000 J

                                               = 2.9 MJ

Part B)

calorific value of gasoline = 47 kJ/g = 47000 kJ/kg

density of gasoline = 900 kg/m^3 = 0.9 kg/L

Mass * calorific value = 2880000 J

Mass = (2880000 / (47000000)) = 0.06127 kg

Volum of gasoline required = mass / density = (0.06127/0.9) = 0.068 L = 7 x 10 ^{- 2} L

Part C)

Generator power output , P = 0.45 kW

Time required to charge battery = energy stored / Power   = (2880000/(0.45*1000) = 6400 s = 1.8 hr