## Differentiation Help!

### Roberto

Posted 01 October 2010 - 05:17 PM

Hi, i was wondering if anyone could help me? I'm stuck on a couple of questions and am completely lost as to what to do.

i) The circumference C cm, of the largest ripple on the surface of a pond after a stone hits it is given by C(t)=2pi root t, where t is the time in seconds after the start of the experiment. Calculate the rate of change of the circumference 4 seconds after the stone hits the water.

ii) The current I amps in an electrical circuit is given by I( R )= 200/R, where R is the resistance in ohms. Find the rate of change of I with respect to R when the resistance is 10 ohms.

I could really use the help.

### Physics and Maths Tutor

Posted 01 October 2010 - 07:05 PM

C(t) = 2pi*t^

dC(t)/dt = 2pi*(1/2)t^

at t=4, dC(t)/dt = pi/root 4 = pi/2

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^{1/2}dC(t)/dt = 2pi*(1/2)t^

^{-1/2}= pi/root tat t=4, dC(t)/dt = pi/root 4 = pi/2

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