JEE Main2014MathematicsApplication of DerivativesActual
If the volume of a spherical ball is increasing at the rate of 4 π cc / sec then the rate of increase of its radius in cm / sec , when the volume is 288 π cc is
Options
- A1 9
- B1 6
- C1 2 4
- D1 3 6
Correct answer
D. 1 3 6
Step-by-step solution
Volume of sphere of radius r is V = 4 3 π r 3 Given V = 288 π   cc ⇒ 288 π = 4 3 π r 3 ⇒ r 3 = 288 × 3 4 = 216 ⇒ r = 6   cm . Again, V = 4 3 π r 3 Differentiate w.r.t. ' t ' ⇒ d V d t = 4 π r 2 d r d t Put the given values, to get ⇒ 4 π = 4 π × 6 2 × d r d t ⇒ d r d t = 1 3 6   cm / sec .