Question

If the radius of a circle is increasing at the rate of 0.5 cm/s, then the rate of increase of its circumference is:

• (A) \( rac{2\pi}{3} \) cm/s
• (B) \( \pi \) cm/s
• (C) \( rac{4\pi}{3} \) cm/s
• (D) \( 2\pi \) cm/s

Answer 1

The Correct Option is B

Step 1: Understand the given data
The radius of the circle is increasing at the rate of 0.5 cm/s. We need to find the rate of increase of the circumference.

Step 2: Recall the formula for circumference of a circle
The circumference C of a circle with radius r is given by:
C = 2πr

Step 3: Differentiate circumference with respect to time
Differentiate both sides with respect to time t:
dC/dt = 2π × dr/dt

Step 4: Substitute the given rate of change of radius
Given dr/dt = 0.5 cm/s, substitute into the differentiated equation:
dC/dt = 2π × 0.5 = π cm/s

Step 5: Conclusion
The rate of increase of the circumference is π cm/s.

Final Answer: (B) π cm/s