Related rates of change

[charlie2002]

Hey,
I've been stuck on this homework problem below and was wondering if anyone can help:

Oil is leaking onto a floor and forms a circular pool. The rate of increase of the radius of the pool, dr/dt = 20cm/min. Calculates the rate at which the area of the pool is increasing dA/dt when the radius is 6cm.

I identified the solution is dA/dt = dr/dt * dA/dr
I have dr/dt as it is stated in the question, the problem is that i don't have dA/dr, I think I need to link area and radius together using A =pi*r^2
But yeah have no clue from here on so someone please help, thanks.

for reference the question is from Nelson Qmaths 12 specialists chapter 9.02 question 4

 

[Deleted member 4993]

Hey,
I've been stuck on this homework problem below and was wondering if anyone can help:

Oil is leaking onto a floor and forms a circular pool. The rate of increase of the radius of the pool, dr/dt = 20cm/min. Calculates the rate at which the area of the pool is increasing dA/dt when the radius is 6cm.

I identified the solution is dA/dt = dr/dt * dA/dr
I have dr/dt as it is stated in the question, the problem is that i don't have dA/dr, I think I need to link area and radius together using A =pi*r^2
But yeah have no clue from here on so someone please help, thanks.

for reference the question is from Nelson Qmaths 12 specialists chapter 9.02 question 4

You say:

I think I need to link area and radius together using

A =pi*r^2 ............................................................................(1)

Yes - correct. Are you saying that you don't know how to calculate dA/dr from the above relation (1)?