A weight is hung over a pulley and attached to a string composed of two parts, each made of the same material but one having four times the diameter of the other. The string is plucked so that a pulse moves along it, moving at speed v1 in the thick part and at speed v2 in the thin part. What is v1 /v2 ?

PINK: 2

YELLOW: 1/2

GREEN: 1/4