A constant external torque τ acts for a very brief period Δt on a rotating system having moment of inertia I. (i) The angular momentum of the system will change by τΔt (ii) The angular velocity of the system will change by (τΔt)/I. (iii) If the system was initially at rest, it will acquire rotational kinetic energy (τΔt)^2/2I. (iv) The kinetic energy of the system will change by (τΔt)^2I.