This isn't actually a homework/schoolwork question, but all the stickies on the other boards say that anything that is a school-work *type* question should go here. Not sure if this qualifies, but I figured I'd err on the side of caution. I took physics II last year and now I'm trying to do a little electronics project -- and to my consternation it appears I didn't learn how to compute something pretty simple!(adsbygoogle = window.adsbygoogle || []).push({});

Suppose I know the total resistance of components in a circuit. In my case it's R = 2292 Ohms. And suppose I've got a battery with an EMF of 14.8 V. How would I find out the time it would take for my battery to run down? Do I need more information? It seems my most relevant equation is that for power delivered to a resistor: [tex] P = V_{ab} = I^2R = (V_{ab})^2 /R [/tex]

However, I don't want the power, which is the work/time, I just want the time. I don't know how I would find out the work that's done. the circuit elements are four motors which are labeled "90W", but I don't know if that means they require 90W every second, or what. How do I find a "t" variable in this equation that I can solve for?

Thanks!

1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

**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!

# How long will a battery last?

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