CUET · MATHS · PYQ PAPER 2025
The radius of spherical balloon is decreasing at the rate of \(0.1 cm / sec\), the rate at which its volume is decreasing, when its radius is 0.5 cm is:
- A \(\frac{\pi}{100} cm^3 / sec\)
- B \(\frac{\pi}{10} cm^3 / sec\)
- C \(\pi\) \(cm ^3 / sec\)
- D \(\frac{2 \pi}{5} cm^3 / sec\)
Answer & Solution
Correct Answer
(B) \(\frac{\pi}{10} cm^3 / sec\)
Step-by-step Solution
Detailed explanation
\( V = \frac{4}{3} \pi r^3 \) \( \frac{dV}{dt} = 4 \pi r^2 \frac{dr}{dt} \) \( \frac{dV}{dt} = 4 \pi (0.5)^2 (-0.1) \) \( \frac{dV}{dt} = -0.1 \pi = -\frac{\pi}{10} cm^3 / sec \) Rate of decrease \( = \frac{\pi}{10} cm^3 / sec \)
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