972 views

### The radius of a circular disc is increasing at a constant rate of 0.003cm/s. Find the rate at which the area is increasing when the radius is 20cm.

The rate at which the area is increasing, dA/dt, can be written with terms we know or can find out easily: dA/dt=dA/dr x dr/dt.

Area of a disc, A = (pi)r^2

dA/dr=2(pi)r

Rate of change of radius, dr/dt=0.003cm/s

Therefore, dA/dt=2(pi)r x 0.003

= 2(pi) x 20 x 0.003

=0.12(pi)

= 0.377cm^2/s

1 year ago

Answered by Henry, an A Level Maths tutor with MyTutor

## Still stuck? Get one-to-one help from a personally interviewed subject specialist

#### 434 SUBJECT SPECIALISTS

£20 /hr

Degree: Veterinary Science (Bachelors) - Bristol University

Subjects offered:Maths, Science+ 5 more

Maths
Science
Physics
Chemistry
Biology
-Personal Statements-

“Veterinary student at the University of Bristol with a background in science and maths, and experience in a summer language school.”

£20 /hr

Degree: Mechanical Engineering (Masters) - Exeter University

Subjects offered:Maths, Chemistry

Maths
Chemistry

“Mechanical Engineering student who has a confident ability to teach Maths and Chemistry.”

MyTutor guarantee

£20 /hr

Degree: Mathematics (Masters) - Bath University

Subjects offered:Maths, Further Mathematics

Maths
Further Mathematics

“Hi! I am studying Mathematics at Bath University and I am passionate about teaching, and learning mathematics.”

MyTutor guarantee

|  1 completed tutorial

Currently unavailable: for regular students

Degree: Materials Science (Masters) - Oxford, The Queen's College University

Subjects offered:Maths, Further Mathematics

Maths
Further Mathematics

MyTutor guarantee

### You may also like...

#### Other A Level Maths questions

How would you integrate ln(x) with respect to x?

How do you prove that (3^n)-1 is always a multiple of 2?

Pushing a mass up a slope and energy

If n is an integer prove (n+3)^(2)-n^(2) is never even.

We use cookies to improve your site experience. By continuing to use this website, we'll assume that you're OK with this.