A thin, uniform $3\mathrm{.}90$ kg

bar, $90\mathrm{.}0$ cm

long, has very small $2\mathrm{.}50$ kg

balls glued on at either end $($Figure $1).$ It is supported horizontally by a thin, horizontal, frictionless axle passing through its center and perpendicular to the bar. Suddenly the right$-$hand ball becomes detached and falls off, but the other ball remains glued to the bar.

Figure$1$ of $1$

The figure shows a thin bar with $2$ small $2\mathrm{.}50-$kilograms balls glued on both sides. An axle goes through the middle of the bar and perpendicular to it$.$

Part A

Find the angular acceleration of the bar just after the ball falls off.

Express your answer in radians per second squared.