After the pilot turns the engine, the blades begin to rotate. At first, they are slow, completing five revolutions in about $5\mathrm{.}00$ seconds. Then, they quickly increase the rate of rotation to $25\mathrm{.}0$ rad$/$s counterclockwise after $10\mathrm{.}0$ seconds. For this question, let's assume the acceleration is constant.

What type of motion is this rotor undergoing?

Non$-$unform circular motion Uniform circular motion $$ Linear motion None of the above

What type of acceleration does this rotor experience?

Centripetal acceleration only Angular acceleration $$ Both centripetal acceleration and angular acceleration Neither centripetal acceleration nor angular acceleration

What is the angular acceleration of the rotor between $5\mathrm{.}00$ and $10\mathrm{.}0$ seconds?

$3\mathrm{.}74$ rad$/$s$22\mathrm{.}50$ rad$/$s$21\mathrm{.}26$ rad$/$s$25\mathrm{.}00$ rad$/$s$2$

Remember, acceleration is still a vector, and we should note its direction. Like angular velocity and position, counterclockwise is considered positive, while clockwise is negative.

In the example above, the helicopter rotors moved counterclockwise and increased in angular speed. The angular acceleration of the rotor was then $---$Select$---$negative$$positive$.$