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 September 29th, 2014, 11:44 PM #1 Senior Member   Joined: Apr 2014 From: UK Posts: 917 Thanks: 331 Joules into a load I have an energy source which when applied accross a 1.2R resistor, drops from 400V to 0V linearly over 2 seconds. I'm trying to work out what integral equation I need to work out the Joules absorbed by the resistor, but it's not apparent to me what it should look like. I've got as far as: Integrate[0 to 2] 400*400/1.2 - something I'm struggling with the something part! Any ideas? September 29th, 2014, 11:53 PM #2 Senior Member   Joined: Apr 2014 From: UK Posts: 917 Thanks: 331 After further though, is it more like: integrate[0 to 2] (400-200x)^2 /1.2 dx ? September 30th, 2014, 06:54 AM #3 Senior Member   Joined: Apr 2014 From: Glasgow Posts: 2,156 Thanks: 731 Math Focus: Physics, mathematical modelling, numerical and computational solutions For an Ohmic resistor, $\displaystyle V = IR,$ $\displaystyle P = IV$ where V, I, R and P are voltage, current, resistance and power respectively. Also, $\displaystyle E = \int^2_0 P(t) dt = \int^2_0 I(t)V(t) dt = \int^2_0 \frac{(V(t))^2}{R}dt$ where E is total energy (in Joules) and $\displaystyle V(t) = 400 - 200t$ can be used as your voltage function. It assumes 100% efficiency and a constant resistance, which are reasonable assumptions for Ohmic resistors. I'll leave it up to you to do the rest Thanks from topsquark and weirddave Last edited by Benit13; September 30th, 2014 at 07:01 AM. October 1st, 2014, 12:17 AM #4 Senior Member   Joined: Apr 2014 From: UK Posts: 917 Thanks: 331 Cheers for that, it's been 15 years since I attempted this sort of thing. If I did it right, I got 240KJ. Tags joules, load Thread Tools Show Printable Version Email this Page Display Modes Linear Mode Switch to Hybrid Mode Switch to Threaded Mode Similar Threads Thread Thread Starter Forum Replies Last Post newercase Algebra 2 May 22nd, 2012 01:33 AM r-soy Physics 2 June 4th, 2011 06:53 PM Marin Advanced Statistics 0 March 30th, 2009 01:23 PM

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