An electric fan rotating at 3 revs-1 is switched off. It comes to rest in 18.0s. Assuming deceleration to be uniform, how many revolutions did it turn before coming to rest?
Correct answer: B. 27 rev
- A. 30 rev
- B. 27 rev
- C. 40 rev
- D. 10 rev
Explanation
ω = angular frequency of the wave. t = time period of the wave.ωi= 3 revωf= 0 rev [ as it is turned off] T = 18 secAngular accelaration a = ωf-ωi/t = 0-3/18 = -1/ 6 Using 2nd equation of motion: θ=ωit + ½ at^2 = [3][18] + 1/ 2[-⅙][18]^2 = 54-27θ= 27 revolutions
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About Angular Displacement
Angular displacement measures the change in a body’s angular position and is expressed in radians or degrees, with anticlockwise and clockwise directions assigned signs. It connects to arc length, angular velocity and angular acceleration, and must be distinguished from ordinary linear displacement in rotational motion.
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