# Rate related derivative problem.

• April 22nd 2008, 09:36 AM
navynukejones
Rate related derivative problem.
The work W done by an electromagnet varies according to W=36t^3-t^2. Find the power dW/dt at t=1/4s.

The answer i got was 6.25. All that i did was take the derivative of 36t^3-t^2 and then plugged in (1/4) for the t. Am i correct in doing this????
• April 22nd 2008, 02:09 PM
elizsimca
Quote:

Originally Posted by navynukejones
The work W done by an electromagnet varies according to W=36t^3-t^2. Find the power dW/dt at t=1/4s.

The answer i got was 6.25. All that i did was take the derivative of 36t^3-t^2 and then plugged in (1/4) for the t. Am i correct in doing this????

Looks good:

$\frac{dW}{dt}=108t^2-2t$

$=108(\frac{1}{4})^2-2(\frac{1}{4})=6.25$