A 12-V car battery is rated at 120 Ah. Assuming that the terminal voltage remains 12 V, for how long can this battery supply power at 29 W? How much charge flows through this battery in this time? How much energy is initially stored in the battery?(adsbygoogle = window.adsbygoogle || []).push({});

I know that an Amp Hour is 3600 C

I know that a Watt is a Joule / s

I know that 1 J= 1C/V

3600 C * 120

So the initial energy stored in the battery is (3600*120) / 12V=36000 Joules

29 Watts=29 J/s

So this battery is delivering 36000 Joules at a rate of 29 J/s

36000/29 = 1241 seconds.

This is only about 20 minutes. This seems very short. I use 7Amp hour batteries at work. I've used them to power a light for a few hours.

So my intuition tells me this answer can't be right.

How much charge flows through the battery during this time? : I=Q/t = 432000 C / 1241 s = 348 Amps. But this assumes I got the seconds correct.

Did I do this right?

**Physics Forums | Science Articles, Homework Help, Discussion**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: Battery (amp hours, total charge, total current)

**Physics Forums | Science Articles, Homework Help, Discussion**