[填空题]
A helicopter rotor blade can be considerelwv )g (:ua4kcd a long t-.c7;exuxyn9x; 3c0 ajqbwjs hin rod, as shown in Fig. 8–4ceb7 x sajy x-qjxc3wun.;;90 6. (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? $m \cdot N$