A particle is to move in an xy plane, clockwise around the origin as seen from the positive side of the z axis. In unit-vector notation, what torque acts on the particle if the magnitude of its angular momentum about the origin is (a) 4.0 kg ⋅ m2/s, (b) 4.0t2 kg ⋅ m2/s, (c) 4.0 √ t kg ⋅ m 2 / s and (d) 4.0/t2 kg ⋅ m2/s?