Question

The radius of a sphere is increasing at a rate of 2 mm/s. How fast is the volume increasing (in mm3/s) when the diameter is 40 mm

Answer 1

Answer:

$\dfrac{dV}{dt}=502.65\ mm^3/s$

Step-by-step explanation:

The volume of a sphere is given by :

$V=\dfrac{4}{3}\pi r^3$

The rate of change of volume means,

$\dfrac{dV}{dt}=\dfrac{d}{dt}(\dfrac{4}{3}\pi r^3)\\\\\dfrac{dV}{dt}=\dfrac{4}{3}\pi \times 3r\times \dfrac{dr}{dt}$

We have, $\dfrac{dr}{dt}=2\ mm/s\ and\ r=40\ mm$

So,

$\dfrac{dV}{dt}=\dfrac{4}{3}\pi \times 3\times 20\times 2\\\\=502.65\ mm^3/s$

So, the volume is increasing at the rate of $502.65\ mm^3/s$.