Question

The rotational speed of blades of a fan reduces from 330 rev/min to 110 rev/min in 4 minutes. Assuming constant deceleration, how long does it take from beginning for blades to stop?​

Answer 1

Given info : The rotational speed of blades of a fan reduces from 330 rev/min to 110 rev/min in 4 minutes.

To find : how long does it take from beginning for blades to stop ?

solution : first we should find the angular deceleration of blades.

using formula, ω = ω₀ + αt

⇒ 110 rev/min = 330 rev/min + α × 4min

⇒ -220 rev/min = 4α

⇒ α = -55 rev/min²

now let's find the time taken to stop the blades from beginning.

again use formula, ω = ω₀ + αt

taking ω = 0 rev/min , ω₀ = 330 rev/min and α = - 55 rev/min²

⇒ 0 = 330 - 55t

⇒ t = 6sec

therefore the time taken to stop the blades of the fan from beginning is 6 sec.