Answer:
0.89534 kgm²
Explanation:
[tex]\omega_f[/tex] = Final angular velocity = 12.9 rad/s
[tex]\omega_i[/tex] = Initial angular velocity = 5.5 rad/s
[tex]I_i[/tex] = Initial moment of inertia = 2.1 kgm²
[tex]I_f[/tex] = Final moment of inertia
As there is no external torque the angular momentum is conserved
[tex]I_i\omega_i=I_f\omega_f\\\Rightarrow I_f=\dfrac{I_i\omega_i}{\omega_f}\\\Rightarrow I_f=\dfrac{2.1\times 5.5}{12.9}\\\Rightarrow I_f=0.89534\ kgm^2[/tex]
The final moment of inertia is 0.89534 kgm²