11.a. If an a-c system requires a 250-hp motor to drive a machine at a uniform rate of speed, what type of motor should be used? A. Induction motor B. Squirrel-cage motor C. Synchronous motor D. Wound-rotor motor 11.b. If a gear unit is used with an a-c motor to increase the speed by a ratio of 4 to 1, then the torque applied to the system is A. increased by 4 to 1. B. decreased by 2 to 1. C. increased by 2 to 1. D. decreased by 4 to 1.

The useful full load torque of a 3-phase 4 pole, 50 Hz induction motor is 162.84 lb-ft.The rotor e.m.f is observed to make 60 cycles per minute. Calculate Motor output Copper loss in rotor Motor input Efficiency if mechanical toque lost in windage and friction is 22.46 lb-ft and stator losses are 850 W

A 100hp, 250 V, 1200 rpm shunt DC motor with an armature resistance of 0.03 Ω and a field resistance of 41.67 Ω. The motor has compensating windings, so armature reaction can be ignored. Mechanical and core losses may be assumed to be negligible for the purposes of this problem. The motor is assumed to be driving a load with a line current of 126 A and an initial speed of 1103 rpm. To simplify the problem, assume that the amount of armature current drawn by the motor remains constant. what is the motor's speed if the field resistance is raised to 50 Ω? can you help me to find N2?

• A 120-V shunt motor has R₁ = 0.25 0 and Rfw = 80 2. The motor takes 4 A at a no-load speed of 1500 rpm. If the motor is to develop a torque of 20 N-m at a speed of 2000 rpm, determine the external resistance that must be added in series with the field winding. (352) • If the rotational loss is proportional to the speed, determine the efficiency and the horsepower rating of the motor at 2000 rpm.