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6. system of particles and rotational motion — Physics STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 SciencePhysics6. system of particles and rotational motion1 Mark
MCQ
A disc is rotating with an angular velocity $\omega _0. $  A constant retrarding torque is applied on it to stop the disc. The angular velocity becomes $(\omega _0/2)$  after $n$ rotations. How many more rotations will it make before coming to rest ?
  • A
    $n$
  • B
    $2n$
  • C
    $\frac {n}{2}$
  • ✓
    $\frac {n}{3}$
✓

Answer

Correct option: D.
$\frac {n}{3}$
d
$w^{2}=w_{0}^{2}-2 \alpha \theta$

$\left(w_{0} / 2\right)^{2}=w_{0}^{2}-2\alpha Q$

$\left(w_{0} / 2\right)^{2}=w_{0}^{2}-2 \alpha Q_{1}$                  

$0=\left(w_{0} / 2\right)^{2}-2 \alpha Q_{2}$

$Q_{2}=\frac{Q_{1}}{3}$

$\Rightarrow \frac {n}{3}$

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