Question

When a ceiling fan is switched off, its angular velocity reduces to 50% while it make 36 rotations. How many more rotations will it make before coming to rest ? (Assume uniform angular retardation)

• A. 18
• B. 12
• C. 36
• D. 48

Answer 1

Answer: (B)

12

Answer 2

$\left( \frac{\omega_{0}}{2} \right)^{2}$ = $\omega_{0}^{2}$ – 2aq

Ž 2a q₁ = $\frac { 3 } { 4 }$ $\omega_{0}^{2}$ ..........(i)

0 = $\left( \frac{\omega_{0}}{2} \right)^{2}$ – 2aq₂ Ž 2aq₂ = $\frac{\omega_{0}^{2}}{4}$ .............(ii)

from (i) & (ii) $\frac{\theta_{1}}{\theta_{2}}$= 3

Ž q₂ = $\frac{\theta_{1}}{3}$ = $\frac{36}{3}$ = 12 rotation