Question

A table fan,rotating at speed of 2400 rpm is switched off and the resulting variation of the rpm with time is shown in fig.The total number of revolutions of the fan before it comes to rest is

Answer 1

The total no. of revolutions is given by the area under the curve

In this diagram rev/min has been converted ti rev/s by dividing each entry on y-axis by 60.Now to calculate the area under the curve:

Area: area of trapezium ABCD +area of triangle DCE

$=\left[\right(\frac{40+10}{2})\times 8]+(\frac{1}{2}\times 16\times 10)$

$=200+80=280$

For complete 280 revolutions before crossing to rest.