Calculus: Early Transcendentals 8th Edition

a) $r=60t$ b) $A(r(t))=3600\pi t^{2}$, the area of the circular ripple as a function of time.
a) Speed of ripple=$\frac{r}{t}=60$ $r=60t$ b) $A(r(t))=\pi r^{2}=\pi (60t)^{2}=3600\pi t^{2}$ This expresses the area of the circular ripple as a function of time.