Physics Vectors & Equilibrium PMDC Conceptual Practice
PMDC Verified Question 30 of 50
If a rigid body is either at rest or rotating with a constant angular velocity, the net external torque acting on the system must be:
A
Maximum
B
Negative
C
Zero
D
Positive
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option C: Zero
Concept:
Rotational equilibrium and its relation to torque.

Formula:
$$\vec{\tau}_{\text{net}} = I \vec{\alpha}$$

Solution:
If a body is at rest or rotating with a constant angular velocity, its angular acceleration \(\vec{\alpha}\) is zero:
$$\vec{\alpha} = \frac{d\vec{\omega}}{dt} = 0$$
Substituting this into Newton's rotational second law yields:
$$\vec{\tau}_{\text{net}} = I(0) = 0$$

Why other options are incorrect:
  • A, B, and D are incorrect because any non-zero net torque (whether positive, negative, or maximum) would produce an angular acceleration, causing the angular velocity to change over time.

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