Question

7. A fan blade is rotating counter-clockwise and slowing down. What are the signs of ? and ??

   A. ? is positive and ? is positive. B. ?ispositiveand?isnegative.   C. ?isnegativeand?ispositive. D. ? is negative and ? is negative. E. ?ispositiveand?iszero.

Answer 1

Whenever a rotating body is slowing down it means that its angular acceleration in acting in opposite direction i.e to slow down a rotating body acceleration will be in opposite direction so as to counter the Velocity.

As angular acceleration = angular velocity /time.

And as we discussed that angular acceleration will be acting in opposite direction hence it will be negative. Now as angular velocity (omega) is still acting in the same direction hence it will be positive. Now due to negative angular acceleration the rotating body will be stopped hence our answer is option B.

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