Connected rates of change?

A watermelon is assumed to be spherical in shape while it is growing. Its mass M kg, and radius r cm, are related by the formula M = kr^3, where k is a constant. It is also assumed that the radius is increasing at a constant rate of 0,1 cm per day. On a particular day the radius is 10 cm and the mass is 3,2kg. Find the value of k and the rate at which the mass is increasing on this day.

1 Answer
Aug 3, 2017

k=2/625,(dM)/dt=0.096" Kg/day"

Explanation:

M=kr^3

"given "r=10" and "M=3.2

rArrk=M/r^3=3.2/1000=2/625

(dM)/dt=(dM)/(dr)xx(dr)/dtlarr" chain rule"

"where "(dM)/(dr)=3kr^2" and "(dr)/dt=0.1

rArr(dM)/dt=3xx2/625xx(10)^2xx0.1

color(white)(rArr(dM)/dt)=0.096" Kg/day"