Question

A table fan rotating at a speed of `2400` rpm is switched off and the resulating variation of the revolution/minute time is shown in Fig. The total number of revolutions of the fan before it comes to rest is

A. `280`
B. `380`
C. `420`
D. `160`

Answer 1

Correct Answer - A
Total number of revolutions = area under `n -t` graph
`= (1)/(2) xx 8 xx (1800)/(60) + 8 xx (600)/(60) + (1)/(2) xx 16 xx (600)/(60)`
`= 120 + 80 + 80 = 280`