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Candee_Puffs
Lv 4
Candee_Puffs asked in Science & MathematicsEngineering · 4 years ago

A 14V d.c. supply is used to charge a 12V car battery of internal resistance 0.80 Ohms for 6.0 hours. The current in the circuit is 2.5A.?

How much electrical energy is provided by the charging supply?

A) 13kJ

B) 110kJ

C) 650kJ

D) 760kJ

I got B. The answer is D but I don t know why...can someone explain how to get to the answer...much appreciated.

2 Answers

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  • Philomel
    Lv 7
    4 years ago

    The resistance is extraneous. 1 j= 1 Ws.

    14*2.5=35 w.

    (6*60)=3600 s

    35*6*3600/=756000j = 756Kj ~

    760>>D

  • Ash
    Lv 7
    4 years ago

    The charging voltage, V = 14V

    current through battery, I = 2.5A

    P = VI = 14 x 2.5 = 35W or 0.035 kW

    t = 6h x (3600 s/1h) = 21600 s

    Energy, E = Pt, where P is in kW and t in seconds

    E = 0.035 x 21600 = 756 kJ

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