Question

A table fan, rotating at a speed of $2400rpm$, 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. $480$
• D. $380$

Answer 1

Answer: (B)

$280$

Area under the curve will be the no of revolution
Area$=\frac{1}{2}\times (40-10)\times 8+(10\times 8)\times \frac{1}{2}\times 10\times (24-8)$ $=120+80+80=280$