NIMCET 2018 — Mathematics PYQ
NIMCET | Mathematics | 2018If the radius of the circle changes at the rate of m/sec, at what rate does the circle's area change when the radius is 10 m?

If the radius of the circle changes at the rate of m/sec, at what rate does the circle's area change when the radius is 10 m?
Concept:
- The area of a circle with r units, is: sq. units.
- The rate of change of the value of a function f(x) with respect to a variable t, is given by: .
- Chain Rule of Derivatives: .
- .
Calculation:
Let's say that the radius of the circle is r meters and let t be the time in seconds.
It is given that m/sec.
Now, Area of the circle: m².
Using the chain rule of derivatives:
When the radius is , the rate of change of area will be: ****.
NOTE: A negative value of the rate of change indicates a decrease.