Jatin Chopra (anonymous) doubts changed status

In the adjacent circuit, AB is a potentiometer wire of length 40 cm and resistance per unit length 50 ohm/m. As shown in the figure, the free end of an ideal voltmeter is touching the potentiometer wire. What should be the speed of the jockey as a function of time so that reading in the voltmeter varies with time as (2sinπt).