NEET 2022 Physics Angular Acceleration MCQ Question

Chapter: System of Particles and Rotational Motion

Class: 11 Physics Topic: Angular Acceleration Difficulty: 🟡 Medium

✅ Ans: D — $4\pi\ \text{rad/s}^2$

Given:

$$\omega_1=1200\ rpm,\qquad \omega_2=3120\ rpm$$

Convert rpm to rad/s:

$$1200\times\frac{2\pi}{60}=40\pi\ rad/s$$ $$3120\times\frac{2\pi}{60}=104\pi\ rad/s$$

Using

$$\alpha=\frac{\omega_2-\omega_1}{t}$$ $$\alpha=\frac{104\pi-40\pi}{16} =\frac{64\pi}{16}$$ $$\boxed{\alpha=4\pi\ rad/s^2}$$

❌ Why other options are wrong?

• A: $12\pi$ ❌ Incorrect conversion/calculation.
• B: $104\pi$ ❌ This is the final angular speed, not acceleration.
• C: $2\pi$ ❌ Incorrect division of angular velocity change by time.
• D: $4\pi$ ✅ Correct.

📌 NCERT Concept

For uniform angular acceleration:

$$\boxed{\alpha=\frac{\Delta\omega}{\Delta t}}$$

Angular velocity must be expressed in rad/s before calculating angular acceleration.

🧠 NEET Trick

$$\boxed{1\ rpm=\frac{\pi}{30}\ rad/s}$$

So directly:

$$\alpha=\frac{(3120-1200)\pi/30}{16} =\boxed{4\pi\ rad/s^2}$$

Note: The screenshot's marked answer A ($12\pi$) is incorrect. The correct answer is D ($4\pi$).