Question

A stone is dropped into some water and a ripple circle of radius r is formed and slowly expands. At the moment the radius is exactly 2m, what rate is the radius of the circle increasing?

Answer 1

The perimeter increases at 3m/s, sorry

Answer 2

what you think

Answer 3

A stone is dropped into some water and a ripple circle of radius r is formed and slowly expands. At the moment the radius is exactly 2m, what rate is the radius of the circle increasing? ` The perimeter increases at 3m/s` <--- is this correct?

Answer 4

A' = 2pi r

Answer 5

"The perimeter increases at 3m/s"

why not use the circumference formula C = 2*pi*r instead of the area formula

Answer 6

yes that would be easier

Answer 7

$$
\Large {C =2\pi r
\\ \frac{dC}{dt} = 2\pi \cdot \frac{dr}{dt}
\\ \therefore \\
3 = 2\pi \cdot \frac{dr}{dt}
\\
\frac{dr}{dt}= \frac{3}{2\pi}

}


$$

it turns out that it does not matter what is the actual radius

Answer 8

sorry internet crashed

Answer 9

still need help