A gymnast with mass m$\_($g$)=49\mathrm{.}0$kg stands on an

improvised balance beam that sits on$,$ but is not attached

to$,$ two supports. The beam has a mass m$\_($b$)=126$kg and

length L$=5\mathrm{.}00$m$.$ Each support is $(1)/(3)$ of the beam's

length from each end.

Initially, the gymnast stands at the left end of the beam.