parallel resistors problem!

[roniG]

Ok two resistors R1 and R2 are connected parallel.

Total resistance is given by R^-1 = R1^-1 + R2^-1

R1 is 80 ohms & increases at 0.3 ohms per sec
R2 is 100 ohms & increases at 0.2 ohms per sec

so the question is now, "how fast is R changing at that time?"

not sure how to go about this question. any help much appreciated

 

[skeeter]

\(\displaystyle \frac{d}{dt} \left( R_T^{-1} = R_1^{-1} + R_2^{-1})\)

take the time derivative (don't forget the chain rule), then solve for \(\displaystyle \frac{dR_T}{dt}\).

 

[Deleted member 4993]

I find it is easier to differentiate:

\(\displaystyle R_t \, = \, \frac{R_1\cdot R_2}{R_1 \, + \, R_2}\)