Posted by Lauren on .
A revolving door consists of four rectangular glass slabs,with the long end of each attached to a pole that acts as the rotation axis. Each slab is 2.60m tall by 1.50m wide and has mass 39.5 .
Find the rotational inertia of the entire door.
If it's rotating at one revolution every 10.5 , what's the door's kinetic energy?

Physics 
Elena,
The moment of inertia (rotational inertia) of the rectangular plate about the axis passing along the axis is
Iₒ=ma²/3, where a= 1.5 m.
Moment of inertia of the whole door is I=4Iₒ=4ma²/3 =4•39.5•1.5²/3=117.9 kg•m².
f=1/10.5=0.095 Hz
KE=Iω²/2=I(2πf)²/2=
=117.9•(2•π•0.095)²/2=21.1 J