[填空题]
A helicopter rotor blade can be conside9y-wn:u(ts ci red a l ,xof fpy+,7swong thin rod, as shown in Fig. 8–4+ fpw,xy7 fs,o6.
(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? $m \cdot N$
