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Question #85399
The Question
An infinitely extended non-conducting solid slab of thickness (in ) has a uniform volume charge density (in ). The slab is fixed at an angle to the horizontal. A solid conducting sphere of mass (in ), radius (in ), and positive charge (in ) is projected directly up the upper surface of the slab with an initial center-of-mass velocity (in ). The coefficient of static friction between the sphere and the slab is . Assume the charge is distributed such that it does not affect the uniform field of the slab, and is sufficiently large for the uncharged sphere to roll. The acceleration due to gravity is (in ) and the permittivity of free space is (in ). Which of the following gives the maximum charge for which the sphere will roll without slipping during its ascent, and the maximum distance it travels up the incline before coming to instantaneous rest?
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
Charged Conducting Sphere|Static Friction Threshold|Mechanical Energy Conservation|Integration
Why This Question Is Tricky
Examiner Levers
Dimensional Analysis
Tests if the student verifies units/dimensions before selecting.
Difficulty Boost : +2Common Mistakes
This question tests the student's ability to couple electrostatics with rigid body dynamics and energy conservation.
The primary trap lies in the Static Friction Threshold: students often forget that an electrostatic force normal to the surface alters the normal force (), which in turn dictates the maximum available static friction ().
A secondary trap is assuming the uniform electric field does work on the sphere as it moves up the incline; however, since the field from an infinite slab is strictly normal to the surface, the electrostatic force does zero work, leaving the stopping distance purely dependent on gravity and initial kinetic energy.
Furthermore, dimensional analysis can eliminate options where the permittivity is incorrectly placed, rewarding students who verify units.
Quick Facts About This Question
Question Information
| Subject | Physics |
| Chapter | Electric Charges and Fields - Class 12 |
| Concept | Charged Conducting Sphere |
| Difficulty | 5 |
| Cognitive Load | 6 |
| Target Solve Time | 140 sec |
| Access | Free |