Question

A fan is running at $3000rpm$. It is switched off. It comes to rest by uniformly decreasing its angular speed in $10seconds$. The total number of revolutions in this period.

• A. $150$
• B. $250$
• C. $350$
• D. $300$

Answer 1

Answer: (B)

$250$

${\omega }_f={\omega }_i+\alpha t$

$0=3000/60+\alpha \left(10\right)$

$\alpha =-5revolutions/s^2$

${\omega }_f^2={\omega }_i^2+2\alpha \Delta \theta$

$0=(3000/60{)}^2+2\times (-5)\times \Delta \theta$

$\Delta \theta =250revolutions$