Q130 / 160 · AP EAMCET 2023 (17 May Shift 2) · Physics

A circular disc of moment of inertia $3.5 \mathrm{~kg} \mathrm{~m}^2$ is rotating with angular speed $30 \mathrm{rad} \mathrm{s}^{-1}$ about an axis passing through its centre and perpendicular to its plane. The torque required to stop the disc in 5 seconds is

  • A
    $84 \mathrm{Nm}$
  • B
    $42 \mathrm{Nm}$
  • C
    $10.5 \mathrm{Nm}$
  • Correct answer
    D
    $21 \mathrm{Nm}$

Solution

Moment of inertia of circular disc, $I=3.5 \mathrm{kgm}^2$ Angular speed, $\omega=30 \mathrm{rad} / \mathrm{s}$ The torque required to stop the disc in 5 seconds $\tau=\frac{\mathrm{I} \omega}{\mathrm{t}}=\frac{3.5 \times 30}{5}=21 \mathrm{Nm}$

Hence, the correct answer is option: 'D'.

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