Explain why heavy luggage should be loaded below passenger seats and why a mechanic would use a long spanner to loosen a stubborn nut.

a) The traffic officer recommended loading luggage below the passenger seats because placing heavy luggage on the roof rack raises the vehicle's center of gravity. A higher center of gravity reduces the vehicle's stability, making it more prone to overturning, especially during turns or sudden braking. Loading luggage lower keeps the center of gravity closer to the ground, thus improving stability and safety.

b) The mechanic used a long spanner because it provides a greater lever arm. According to the principle of torque ($\tau = F \times r$), a longer lever arm ($r$) allows a smaller force ($F$) to generate a larger torque. This makes it easier to loosen or tighten stubborn nuts, as less effort is required from the