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Question #42473

Difficulty: 8/10 | 🟢 Free

The Question

A cylindrical container filled with a liquid of density ρf\rho_f is accelerated vertically upwards with a time-varying acceleration a(t)=αta(t) = \alpha t, where α=4 m/s3\alpha = 4 \text{ m/s}^3. A small sphere of mass m=1 kgm = 1 \text{ kg}, volume VV, and density ρs=ρf/2\rho_s = \rho_f / 2 is released from rest at the bottom of the container at t=0t = 0. The sphere experiences a relative velocity-dependent drag force FD=−bvF_D = -b v, where b=2 kg/sb = 2 \text{ kg/s} and vv is the velocity of the sphere relative to the container. Assuming the container is sufficiently tall, what is the work done by the pseudo force on the sphere in the reference frame of the container during the interval t=0t = 0 to t=1 st = 1 \text{ s}? (Take g=10 m/s2g = 10 \text{ m/s}^2)

Options

  • A.

    −(203+12e−2) J-\left(\frac{20}{3} + 12e^{-2}\right) \text{ J}

  • B.

    −(163+8e−2) J-\left(\frac{16}{3} + 8e^{-2}\right) \text{ J}

  • C.

    (203−12e−2) J\left(\frac{20}{3} - 12e^{-2}\right) \text{ J}

  • D.

    −(103+6e−2) J-\left(\frac{10}{3} + 6e^{-2}\right) \text{ J}

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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

Variable Force Integration|Accelerated Frame Hydrostatics|Integration of Velocity-dependent forces

Why This Question Is Tricky

Common Mistakes

This question tests the mechanics of non-inertial frames combined with variable force integration.

The primary trap lies in assuming the buoyant force remains constant; in an accelerated frame, the pressure gradient depends on the effective gravity geff(t)=g+a(t)g_{eff}(t) = g + a(t), making buoyancy time-dependent.

Furthermore, students often incorrectly calculate the work done by the pseudo force by multiplying the average force by displacement or neglecting it entirely.

The correct approach requires setting up a non-homogeneous differential equation for velocity and explicitly integrating the time-dependent pseudo force Fp(t)=−ma(t)F_p(t) = -ma(t) against the instantaneous velocity v(t)v(t).

Quick Facts About This Question

Question Information

SubjectPhysics
ChapterWork, Energy, and Power - Class 11 Part 1
ConceptVariable Force Integration
Difficulty8
Cognitive Load7
Target Solve Time160 sec
AccessFree