Answer
a. $1.90 \times 10^3 kg \cdot m^2$
b. $8900 N \cdot m$
Work Step by Step
a. The rotational inertia of one rod/blade around an end is $\frac{1}{3}ML^2$. There are three rods.
$$I=3\frac{1}{3}MR^2=(135 kg)(3.75m)^2 \approx 1.90 \times 10^3 kg \cdot m^2$$
b. The angular acceleration is $\alpha=\frac{\Delta \omega}{\Delta t}=4.71 \frac{rad}{s^2}$.
Calculate the torque using $\tau = I \alpha \approx 8900 N \cdot m$.
