A wheel rotates about a fixed axle at its center. A force is applied radially inward at the rim (toward the pivot) while the wheel turns through angle . What can be inferred about the work done by the torque from this force?
- Positive, because the point of application moves along a circular path.
- Negative, because the force points toward the pivot.
- Zero, because the force produces zero torque about the pivot. (correct answer)
- Nonzero, because any force applied at the rim produces torque.
Explanation: This question assesses understanding of work done by torque in rotational motion. Work is calculated as W = τ Δθ, requiring torque through angular displacement. If the torque is zero, no work is done regardless of displacement. A radial force produces zero torque since the lever arm is zero. Choice D is incorrect because not every force at the rim produces torque; radial forces do not. To tackle these, first compute the torque magnitude and direction, then apply the work formula, ensuring no assumptions about force direction.