Question

When a ceiling fan is switched off, its angular velocity fall to half while it makes 36 rotations . How many more rotations will be make before coming to rest ? (Assume uniform angular retardations ). A) 36 B) 24 C) 18 D) 12

Answer 1

Answer:

PHYSICS

When a ceiling fan is switched off, its angular velocity reduces to half its initial value after it completes 36 rotations. The number of rotations it will make further before coming to rest is   Assuming angular retardation to be uniform

A .

10

B .

20

C .

18

D .

12

October 15, 2019Thilakavathy Lakhani

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VIDEO EXPLANATION



ANSWER

1st case:

We can write the equation of motion for circular motion as:

ω2=ω02+2aθn

Now, ω=2ω0,θ=36×2π (given)

So, 4ω02=ωo2+2α×36×2π

So, α=4×144π−3ω02

2nd case:

0=4ω02−2×4×144π3ω02×θ

So, θ=24π

So, number of rotations made by the fan before coming to rest =2π24π=12

D.12