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NEET 2010
Exam
NEET
Year
2010
Subject
Physics
Chapter
Laws of Motion

NEET 2010 · Physics · Laws of Motion

A gramophone record is revolving with an angular velocity ω . A...

A gramophone record is revolving with an angular velocity ω\omega. A coin is placed at a distance r\mathrm{r} from the centre of the record. The static coefficient of friction is μ\mu. The coin will revolve with the record if

Options

  1. Ar=μgω2\mathrm{r}=\mu g \omega^2
  2. Br<ω2μg\mathrm{r} < \frac{\omega^2}{\mu g}
  3. Cr≤μgω2r \leq \frac{\mu g}{\omega^2}
  4. Dr≥μgω2r \geq \frac{\mu g}{\omega^2}

Correct answer

C. r≤μgω2r \leq \frac{\mu g}{\omega^2}

Step-by-step solution

When the disc spins the frictional force between the gramophone record and coin is μmg\mu \mathrm{mg} The coinwillrevolvewithrecord,ifcoin will revolve with record, ifFfrictional ≥Fcentripetal μmg≥mω2rμgr≥ω2\begin{aligned} F_{\text{frictional }} & \geq F_{\text{centripetal }} \\ \mu m g & \geq m \omega^2 r \\ \frac{\mu g}{r} & \geq \omega^2 \end{aligned}$$
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