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Question #42428
The Question
A block of mass rests on a smooth horizontal table. A long, light string of linear mass density is attached to the block, passes around a light movable pulley, and has its other end fixed to a vertical wall. The string segments are horizontal. At , the movable pulley is pulled away from the wall with a time-varying acceleration . At the exact same instant , a transverse wave pulse is generated at the block. The initial distance between the block and the pulley is . Assuming the tension is uniform along the string at any given instant, find the time when the pulse reaches the pulley.
Options
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- D.
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Correct Answer
Step-by-Step Solution
Explanation
How the Examiner Thinks
Variable_Constraint
Develop pure symbolic logic skills by mastering algebraic constraints without relying on numerical data.
Concepts Behind This Question
Constraint Relations via String Length|String Tension and Wave Speed|Partial Differentiation
Why This Question Is Tricky
Common Mistakes
This problem tests the synthesis of non-inertial wave dynamics and kinematic constraints.
The primary trap is the assumption of a quasi-static or constant wave speed.
Students must first use constraint relations to find the block's acceleration, which dictates a time-varying tension and thus a modulating wave speed .
The secondary, more fatal trap is integrating and equating it to the initial length .
Students must realize that the string itself acts as a moving medium () and the target boundary (the pulley) is also accelerating ().
The correct formulation requires transforming the wave speed into the lab frame and equating the absolute dynamic positions of the pulse and the pulley.
Quick Facts About This Question
Question Information
| Subject | Physics |
| Chapter | Laws of Motion - Class 11 Part 1 |
| Concept | Constraint Relations via String Length |
| Difficulty | 8 |
| Cognitive Load | 7 |
| Target Solve Time | 160 sec |
| Access | Free |