5. 6 m In the helicopter shown, a vertical tail propeller is used to prevent rotation of the cab as the speed of the main blades is changed. Each of the four main blades is assumed to be a 5- m slender rod of mass 30 kg. Assuming that the tail propeller is operating and that the angular velocity of the cab remains zero, determine (a) the final horizontal velocity of the cab when the speed of the main blades is changed from 200 to 300 rpm. The cab has a mass of 720 kg and is initially at rest. Also determine (b) the force exerted by the tail propeller if this change in speed takes place uniformly in 12 seconds. Use the principle of Impulse-Momentum of Rigid Bodies. [Hint: refer to Supplemental Examples for a similar problem.] QIO Final Answers (a) (b)