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Question #42050
The Question
A uniform rigid door of mass and width is hinged at one edge. At , a sensor triggers an automated motor which applies a torque . Due to a reaction time gap of the release latch, the door remains locked and stationary until . At exactly , the latch instantaneously disengages. Assuming no friction in the hinge, what is the work done by the motor on the door during the interval to ?
Options
- A.
- B.
- C.
- D.
Check Your Answer
Correct Answer
Step-by-Step Solution
Explanation
How the Examiner Thinks
Multi-Concept_Bridge
Master problems that require linking physics and math concepts to solve complex competitive questions.
Concepts Behind This Question
The Reaction Time Gap|Instantaneous Nature|Work-Energy Theorem for Rotation
Why This Question Is Tricky
Common Mistakes
This question tests the student's ability to correctly apply the Work-Energy Theorem in the presence of a reaction time gap and a time-dependent force.
A common trap is blindly integrating the angular acceleration from (ignoring the boundary condition at ), which yields an incorrect angular velocity of and a kinetic energy of .
Another mistake is calculating work as the time integral of torque () rather than the angular displacement integral (), leading to .
The problem enforces the understanding that work is strictly zero when displacement is zero, despite a large applied force, and that kinematic integration must respect the physical release time.
Quick Facts About This Question
Question Information
| Subject | Physics |
| Chapter | Motion in a Straight Line - Class 11 Part 1 |
| Concept | The Reaction Time Gap |
| Difficulty | 8 |
| Cognitive Load | 7 |
| Target Solve Time | 160 sec |
| Access | Free |