Question

A table fan, rotating at a speed of $2400 \, \, \text{r} \text{p} \text{m}$ is switched off and the resulting variation of the rpm with time is shown in the figure. The total number of revolutions of the fan before it comes to rest is

• A. $420$
• B. $280$
• C. $240$
• D. $380$

Answer 1

Answer: (B)

$280$

Answer 2

Number of revolutions = area under the curve no. of revolution $= \frac{1}{2} \times \left(\frac{2400}{60} + \frac{600}{60}\right) \times 8 + \frac{1}{2} \times \frac{600}{60} \times 16$ no. of revolution $= \, 280$