Question

When a ceiling fan is switched off, its angular velocity falls to half while it makes 36 rotations. How many more rotations will it make before coming to rest? (Assume uniform angular retardation.) 

(a) 36 

(b) 24 

(c) 18 

(d) 12

Answer 1

Correct Answer: (d) 12

Let Ω = angular velocity of the fan when it is switched off.

ω_f² = ω_i² + 2αθ

∴ (Ω/2)² Ω² + 2α(2π x 36)

and 0 = (Ω/ 2)² + 2α(2πN).