A circular wave travels such that a crest occurs at radius \(r_{1}\) at instant \(t_{1}\). The same crest has a radius \(r_{2}=2 r_{1}\) at \(t_{2}=2 t_{1}\).

(a) What is the wave speed?

(b) Where is the crest at \(t_{3}=3 t_{1}\) ?

(c) What is the ratio (energy per unit length at \(t_{3}\) )/(energy per unit length at \(t_{1}\) )?