Question

A ceiling fan is turned on and reaches an angular speed of 132 rev/min in 20 s. It is then turned off and coasts to a stop in an additional 40 s. The ratio of the average angular acceleration for the first 20 s to that for the last 40 s is which of the following?

a. 2
b. -0.5
c. 0.5
d. -2

Answer 1

Answer:

Explanation:

α = (ωf - ωi)/t

acceleration phase

ωf = 132 rev/min (2π rad/rev / 60 s/min) = 4.4π rad/s

α₁ = (4.4π - 0)/20 = 0.22π rad/s²

α₂ = (0 - 4.4π)/40 = - 0.11π rad/s²

α₁/α₂ = 0.22π/- 0.11π = -2