Final answer:
a) Primary shoe. In a drum brake system, the primary shoe does 70% of the braking.
Step-by-step explanation:
In a drum brake system, the primary shoe does 70% of the braking.
A drum brake system consists of two curved brake shoes that press against the inside surface of a rotating drum. The primary shoe has a larger lining area and is positioned closer to the wheel cylinder, allowing it to generate more braking force. The secondary shoe, on the other hand, has a smaller lining area and is located farther away from the wheel cylinder.
When the brake pedal is pressed, hydraulic pressure is applied to the wheel cylinder, which pushes the primary shoe against the drum. This causes friction between the shoe and drum, resulting in braking force. Due to its larger lining area and closer proximity to the wheel cylinder, the primary shoe is responsible for 70% of the braking, while the secondary shoe contributes the remaining 30%.