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Question #43932

Difficulty: 8/10 | 🟢 Free

The Question

A block of mass m=1 kgm = 1 \text{ kg} is released from rest and slides down a rough inclined plane of angle θ=30∘\theta = 30^\circ. A small generator attached to the block produces an electrical power P=cv2P = c v^2, where vv is the instantaneous velocity of the block and c=0.2 W⋅s2/m2c = 0.2 \text{ W}\cdot\text{s}^2/\text{m}^2. This power is entirely dissipated as heat by a coil embedded in the bottom surface of the block. The coefficient of kinetic friction between the block and the incline decreases with the dissipated power as μk=μ0−kP\mu_k = \mu_0 - k P, where μ0=123\mu_0 = \frac{1}{2\sqrt{3}} and k=1203 W−1k = \frac{1}{20\sqrt{3}} \text{ W}^{-1}. Assuming the thermal response is instantaneous, what is the kinetic energy of the block after it has slid a distance d=10 md = 10 \text{ m} down the incline? (Take g=10 m/s2g = 10 \text{ m/s}^2)

Options

  • A.

    25(e−1) J25(e - 1) \text{ J}

  • B.

    25 J25 \text{ J}

  • C.

    25(1−e−1) J25(1 - e^{-1}) \text{ J}

  • D.

    50(e−1) J50(e - 1) \text{ J}

Check Your Answer

Correct Answer

Step-by-Step Solution

Explanation

How the Examiner Thinks

Intuition_Breaker

Train your brain to resist "obvious" answers that are designed to deceive your intuition.

Concepts Behind This Question

Cell EMF vs Terminal Voltage|Kinetic Friction Transition|Binomial Approximation

Why This Question Is Tricky

Common Mistakes

The core trap tests the student's ability to handle dynamically coupled non-conservative forces.

A common mistake is treating the work done by friction as a simple macroscopic average or ignoring the velocity dependence entirely (yielding 25 J).

Another trap is a sign error when substituting the decreasing friction into the net force equation, leading to an exponentially decaying acceleration profile instead of an exponentially growing one (yielding 25(1 - e^-1) J).

This question forces the application of the Work-Energy Theorem in its differential form (dK = F_net dx) and tests the mathematical translation of a physical feedback loop (velocity -> power -> heat -> friction -> acceleration -> velocity).

Quick Facts About This Question

Question Information

SubjectPhysics
ChapterCurrent Electricity - Class 12
ConceptCell EMF vs Terminal Voltage
Difficulty8
Cognitive Load7
Target Solve Time160 sec
AccessFree