At t$=0$

the current to a dc electric motor is reversed, resulting in an angular displacement of the motor shaft given by $\backslash$theta $($t$)=($

$250$ rad$/$s

$)$t$($

$19\mathrm{.}7$ rad$/$s$2$

$)$t$2($

$1\mathrm{.}41$ rad$/$s$3$

$)$t$3$

$.$At what time is the angular velocity of the motor shaft zero?

Express your answer in seconds.Part B

Calculate the angular acceleration at the instant that the motor shaft has zero angular velocity.

Express your answer in radians per second squared.Part C

How many revolutions does the motor shaft turn through between the time when the current is reversed and the instant when the angular velocity is zero?

Express your answer in revolutions.Part D

How fast was the motor shaft rotating at t$=0$

$,$ when the current was reversed?

Express your answer in radians per second.Part E

Calculate the average angular velocity for the time period from t$=0$

to the time calculated in part A$.$

Express your answer in radians per second.