Question

# A fan is running at $$3000\ rpm$$. It is switched off. It comes to rest by uniformly decreasing its angular speed in $$10\ seconds$$. The total number of revolutions in this period.

A
150
B
250
C
350
D
300

Solution

## The correct option is D $$250$$$$\omega_f = \omega_i + \alpha t$$$$0 = 3000 / 60 + \alpha (10)$$$$\alpha = -5 \ revolutions/s^2$$$$\omega_f^2 = \omega_i^2 + 2 \alpha \Delta \theta$$$$0 = (3000/60)^2 + 2 \times (-5) \times \Delta \theta$$$$\Delta \theta = 250\ revolutions$$Physics

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