Fundamentals of Automotive Systems

A: Governing principle: Brake discs are heat sinks first, friction pairs second. Applied here: GG25 has high specific heat and thermal conductivity, tolerates 500–600 °C without phase change, and fits cost and packaging; the mass penalty is acceptable at this axle. Trap: Engineers who know unsprung mass hurts ride often grab aluminum, missing that anodized layers fail under repeated 400+ °C stops in real traffic.

A: Governing principle: Pressure equals force divided by piston area. Applied here: 300 N × 4.5 gives 1350 N at the master; area of a 20 mm bore is 3.14×10⁻⁴ m², yielding roughly 4.3 MPa or 43 bar. Trap: Dropping the pedal ratio or doubling pressure by mixing up radius and diameter lands people at 21 or 85 bar.

A: Governing principle: Dissimilar metals plus electrolyte create a galvanic cell. Applied here: Chloride solution bridges zinc‑plated steel and aluminum, making the aluminum anodic and producing pitting and white hydroxides in stagnant zones. Trap: Engineers familiar with fretting in bearings may over‑apply it here, ignoring the visible electrochemical signature.

A: Governing principle: Mechanical power equals torque times angular speed. Applied here: 800 W / 0.55 ≈ 1450 W mechanical; at 800 rpm (≈84 rad/s) torque is about 17 N·m, close to 20 N·m. Trap: Forgetting efficiency or using rpm directly without converting to rad/s drags people to 5 or 60 N·m.