MCQ
A flywheel rotates about an axis. Due to friction at the axis, it experiences an angular retardation proportional to its angular velocity. If its angular velocity falls to half while it makes $n$ rotations, how many more rotations will it make before coming to rest?
  • A
    $2n$
  • $n$
  • C
    $n/2$
  • D
    $n/3$

Answer

Correct option: B.
$n$
b
$\alpha \,is\,propotional\,to\,\omega $

$Let = \alpha  = k\omega $                       ($k$ is constant)

$\frac{{d\omega }}{{dt}} = k\omega \,\,\,\,\,\,\,\,\,\left[ {also\,\frac{{d\theta }}{{dt}} = \omega  \Rightarrow dt = \frac{{d\theta }}{\omega }} \right]$

$\therefore \frac{{\omega d\omega }}{{d\theta }} = k\omega  \Rightarrow d\omega  = kd\theta $

$Now\,\int\limits_\omega ^{\omega /2} {d\omega  = k\int {d\theta } } $

$\int\limits_{\omega /2}^0 {d\omega  = k\int\limits_0^\theta  {d\theta  \Rightarrow  - \frac{\omega }{2} = k\theta  \Rightarrow  - \frac{\omega }{2} = K{\theta _1}} } $

$\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\left( {{\theta _1} = 2\pi n} \right)$

$\therefore \theta  = {\theta _1}\,\,or\,\,2\pi {n_1} = 2\pi n$

${n_1} = n$

Need a full question paper?

Generate a complete, print-ready paper with questions like this in minutes — across 16+ boards, with answer keys.

Start Generating Free

Similar questions

In simple harmonic motion, the total mechanical energy of given system is E. If mass of oscillating particle P is doubled then the new energy of the system for same amplitude is :

Image
A small lamp is hung at a height of $ 8$ feet above the centre of a round table of diameter $16 $ feet. The ratio of intensities of illumination at the centre and at points on the circumference of the table will be
By Huygen's wave theory of light, we cannot explain the phenomenon of
The displacement $y$ (in $cm$) produced by a simple harmonic wave is $y = \frac{{10}}{\pi }\sin \left( {2000\pi t - \frac{{\pi x}}{{17}}} \right)$. The periodic time and maximum velocity of the particles in the medium will respectively be
${T}_{0}$ is the time period of a simple pendulum at a place. If the length of the pendulum is reduced to $\frac{1}{16}$ times of its initial value, the modified time
The dispersion for a medium of wavelength $\lambda$ is $D$, then the dispersion for the wavelength $2 \lambda$ will be
When a force of constant magnitude and a fixed direction acts on a moving object, then its path is
A physical quantity $z$ depends on four observables $a,$ $b,$ $c$ and $d ,$ as $z =\frac{ a ^{2} b ^{\frac{2}{3}}}{\sqrt{ c } d ^{3}} .$ The percentage of error in the measurement of $a, b, c$ and $d$ are $2 \%, 1.5 \%, 4 \%$ and $2.5 \%$ respectively. The percentage of error in $z$ is$......\%$
An engine approaches a hill with a constant speed. When it is at a distance of $0.9\, km$, it blows a whistle whose echo is heard by the driver after $5\, seconds$. If the speed of sound in air is $330\, m/s$, then the speed of the engine is .... $m/s$
While a collector to emitter voltage is constant in a transistor, the collector current changes by $8.2\, mA$ when the emitter current changes by $8.3\, mA.$ The value of forward current ratio hfe is