## Calculus (3rd Edition)

The velocity decreases at a rate of $8$ x $10^{-5}\ cm/sec$.
$v = 6.4 * 10^{-8} - 0.001r^2$ To find the rate of change, we have to find the derivative f the function which we can do using the power rule: $v' = -0.002r$ Now we substitute r=0.004 into the equation to find the rate of change at that specific point: $v' = -0.002(0.004) = -0.00008$ To interpret this answer, we note that the number is negative and so the velocity decreases at a rate of $8$ x $10^{-5}\ cm/sec$