[填空题]
A helicopter rotor b)5 oxhqb (psz(lade can be considered 3oh/)us rwj4n .cv7nd a long thin rod, as shown in Fig. 8–46ov/wh4csj 7n3r)n.u d . (a) If each of the three rotor helicopter blades is 3.75 m long and has a mass of 160 kg, calculate the moment of inertia of the three rotor blades about the axis of rotation. $kg \cdot m^2$ (b) How much torque must the motor apply to bring the blades up to a speed of 5 $rev/s$ in 8.0 s? $m \cdot N$