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Concepts Of Physics MCQ Edition [Volume 1]
Exam
Concepts Of Physics MCQ Edition [Volume 1]
Subject
Physics
Chapter
Rotational Mechanics

Concepts Of Physics MCQ Edition [Volume 1] · Physics · Rotational Mechanics

A flywheel with a moment of inertia of 5.0 kg-m^2 is rotated at a...

A flywheel with a moment of inertia of 5.0 kg-m25.0 \text{ kg-m}^2 is rotated at a speed of 60 rad/s60 \text{ rad/s}. Due to friction at the axle, it comes to rest in 5.0 minutes5.0 \text{ minutes}. Determine the total work done by the friction.

Options

  1. A3.0 kJ3.0 \text{ kJ}
  2. B4.5 kJ4.5 \text{ kJ}
  3. C9.0 kJ9.0 \text{ kJ}
  4. D18.0 kJ18.0 \text{ kJ}

Correct answer

C. 9.0 kJ9.0 \text{ kJ}

Step-by-step solution

Initial kinetic energy of the flywheel is given by Ki=12Iωi2K_i = \dfrac{1}{2} I \omega_i^2.

Substituting the given values, I=5.0 kg-m2I = 5.0 \text{ kg-m}^2 and ωi=60 rad/s\omega_i = 60 \text{ rad/s}:

Ki=12×5.0×(60)2K_i = \dfrac{1}{2} \times 5.0 \times (60)^2

Ki=12×5.0×3600=9000 JK_i = \dfrac{1}{2} \times 5.0 \times 3600 = 9000 \text{ J}

Final kinetic energy Kf=0K_f = 0 since the flywheel comes to rest.

According to the work-energy theorem, the total work done by friction is equal to the change in kinetic energy:

W=Kf−Ki=0−9000 J=−9000 JW = K_f - K_i = 0 - 9000 \text{ J} = -9000 \text{ J}

The magnitude of the total work done by friction is 9.0 kJ9.0 \text{ kJ}.
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