alleryStart learning →A robot joint is turning and its angular velocity is falling steadily. What is the sign of its angular acceleration?
APositive, because it is still turning
BZero, because the axis does not move
CPositive, because the radius is positive
DNegative, because angular velocity falls
Answer & Solution
Correct answer: D. Negative, because angular velocity falls
1. Angular acceleration is alpha = delta omega / delta t, so its sign follows the sign of delta omega.
2. If omega increases, alpha is positive, and if omega decreases, alpha is negative.
3. Here the angular velocity is falling, so delta omega is negative and alpha is negative.
4. Still turning is not the test, since a body can spin fast while slowing down hard.
_Source: OpenStax College Physics (CC BY 4.0), Ch 10 "Rotational Motion and Angular Momentum", section 10.1 Angular Acceleration_
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