At time t, r = 4.0t2i - (2.0t + 6.0t2) j gives the position of a 3.0 kg particle relative to the origin of an xy coordinate system (r is in meters and t is in seconds).
(a) Find an expression for the torque acting on the particle relative to the origin.
(b) Is the magnitude of the particle's angular momentum relative to the origin increasing, decreasing, or unchanging?