A 10-hp (7.46 kW), 250-V. shunt motor takes a line current of 5 A. when running light. Calculate the efficiency when delivering full load output, if the armature and field resistances are 0.5 Ω and...

A 10-hp (7.46 kW), 250-V. shunt motor takes a line current of 5 A. when running
light. Calculate the efficiency when delivering full load output, if the armature and
field resistances are 0.5 Ω and 250 Ω respectively. At what output power will the
efficiency be maximum?