control system lab

this is my lab experiment result.hope someone can guide me to solve it.

1. set the scale on the attenuator unit to zero.set the switch on the operational amplifier unit to the 100k resistor.

2switch on the power supplly and if the motor rotates continously, vary the zero set on the operational amplifier unit until the motor stop.

3.vary the scale on the attenuator unit so that the motor speed is at 1000rpm.

4.input voltage 276v

motor speed-brake scale

970-10

980-8

900-4

980-2

1000-0

the question is

1.calculate the percentage regulation for the brake setting at scale 9.

2. explain why the motor does not stop when the input voltage is zero.

this is an experiment of closed loop speed control system.