(a) State the principle of conservation of momentum. (b) The propulsion system of a toy car consists of a propeller attached to an electric motor, as illustrated in Fig. 3.1. [Figure 3.1] The car is on horizontal ground and is initially held at rest by its brakes. When the motor is switched on, it rotates the propeller so that air is propelled horizontally to the left. The density of the air is 1.3 kg m⁻³. Assume that the air moves with a speed of 1.8 ms⁻¹ in a uniform cylinder of radius 0.045 m. Also assume that the air to the right of the propeller is stationary.