In: Physics
You are handed a rod that is three times as dense on one end as it is on the other end. Find the moment of inertia when the axis of rotation is about the heavy end, and find the moment of inertia when the axis of rotation is about the light end.
the linear density may be changes from
to 3
then
( x ) =
( 1 +
2x/L )
the moment of inertia of the lighter end is
ILighter = 
( x )
x2 dx
ILighter = 5
L3 /
6
the total mass is M = 
( x ) dx
= 2
L
so
the moment of inertia when the axis of rotation is about the light end is ILighter = 5 M L2 / 12
the moment of inertia of heavier end is
x = ( L - x )
so
Iheavier = 
( L - x )
x2 dx
so
the moment of inertia when the axis of rotation is about the heavy end is Iheavier = M L2 / 4