Question

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

• A. 160
• B. 280
• C. 380
• D. 420

Answer 1

Answer: (B)

280

Answer 2

Total number of revolutions $=$ area under $n-t$ graph $=\frac{1}{2} \times 8 \times \frac{1800}{60}+8 \times \frac{600}{60}+\frac{1}{2} \times 16 \times \frac{600}{60}$ $=120+80+80=280$