Correct Answer is: (b) mk2r2t
ac = k 2rt 2 = v 2/r or v = krt.
The tangential acceleration is at = dv / dt = kr.
∴ the net tangential force on the particle = mat = mkr = Ft.
Work is done on the particle only by tangential forces, as the radial forces are perpendicular to v.
∴ the power delivered to the particle = Ftv = (mkr)(krt) = mk 2r 2t.
