Rate of change of surface area of a sphere given the rate of change of the radius Air is pumped into a spherical balloon such that the radius of the balloon increases at the rate of 1/20pi cm/s when the radius is 8.5cm. Find the rate of change of the surface area of the balloon at this instant. How do I do this? I still don't really understand how rate of change works here.

patylomy7

patylomy7

Answered question

2022-08-10

Rate of change of surface area of a sphere given the rate of change of the radius
Air is pumped into a spherical balloon such that the radius of the balloon increases at the rate of 1 20 π cm/s when the radius is 8.5cm. Find the rate of change of the surface area of the balloon at this instant.
How do I do this? I still don't really understand how rate of change works here.

Answer & Explanation

Deja Navarro

Deja Navarro

Beginner2022-08-11Added 17 answers

The surface area S is related to the radius r via
(1) S = 4 π r 2 ;
thus, S ˙ is related to r ˙ via
(2) S ˙ = 8 π r r ˙ ;
when
(3) r = 8.5 cm.
and
(4) r ˙ = 1 20 π cm./sec. ,
we have
(5) S ˙ = 8 π ( 8.5 ) 1 20 π = 68 20 cm.^2/sec. = 17 5 cm.^2/sec. .

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