Auto Information Practice Test 5: Electrical and Charging

Answer: A

Correct answer: Rotor. Friction brakes rub a stationary part against a part that turns with the wheel. In a disc brake the turning part is the rotor, while the caliper and its pads stay fixed and clamp it.

• A (correct): The rotor, or disc, is fastened to the hub and spins with the wheel while the pads squeeze it.
• B: The caliper straddles the rotor and holds the pistons, but it does not rotate with the wheel.
• C: Pads are held by the caliper and stay stationary while rubbing on the turning rotor.
• D: A backing plate is the fixed mounting for the shoes in a drum brake, and it does not turn.

Answer: B

Correct answer: Through a ground wire or mounting into the metal body, then to battery negative. Most vehicles use negative ground: the battery negative cable bolts to the engine and body, so the metal structure acts as the return conductor. The headlamp's current flows through its ground wire or mount into the body and back to battery negative, and that return path is part of the circuit.

• A: Current must flow around a complete loop; a lamp converts energy, not charge.
• B (correct): The body and engine are bonded to battery negative, so the metal structure serves as the shared return path.
• C: One wire cannot carry current both out and back; the return needs its own path.
• D: A rubber drive belt is not an electrical path; the return goes through the body and ground cable to battery negative.

Answer: B

Correct answer: Shock absorbers, struts and other suspension parts for wear. Scooped dips around the tread are cupping, or scalloping, often felt as rhythmic noise or vibration. It usually suggests worn shocks or struts, loose suspension parts or long-running imbalance, so new tires alone may soon cup again unless the cause is fixed.

• A: Age matters for safety, but it does not explain a cupping pattern.
• B (correct): Cupping commonly points to worn shocks or struts, loose suspension parts or long-running imbalance.
• C: The traction grade is a test result and has nothing to do with this wear pattern.
• D: The spare is worth checking routinely, but it does not cause cupping on the road tires.

Answer: C

Correct answer: When the two drive wheels turn at different speeds, as in a turn. In a turn the outside wheel travels a longer arc than the inside wheel and must turn faster. The spider gears spin on their shaft to let one side gear speed up while the other slows down. Going straight, everything turns together as a unit.

• A: Going straight, both axles turn at carrier speed and the spider gears ride along without spinning on their shaft.
• B: Reverse changes the direction of the whole carrier; it does not by itself make the spider gears spin on their shaft.
• C (correct): Spider gears rotate on their shaft only when one side gear must turn faster than the other.
• D: With the vehicle stopped, the carrier and axles are not turning, so the spider gears are not working.

Answer: C

Correct answer: The sensor under-reports airflow, so the mixture runs lean. A hot-film MAF sensor measures air mass by how much the passing air cools its heated element. Contamination reduces that cooling, so the sensor under-reports airflow, the ECM calculates too little fuel and the engine tends to run lean.

• A: A coated element is cooled less by the passing air, so it reads low, not high.
• B: A MAF sensor reports airflow for fueling; a dirty element does not lock spark timing.
• C (correct): The contamination insulates the element, the ECM thinks less air is entering, and it injects too little fuel for the real airflow.
• D: Pump pressure is not set by the MAF reading, and higher pressure would not follow from a dirty air sensor.

Answer: C

Correct answer: 0W-20, because the lower number before the W means better cold flow. Compare the numbers before the W, which rate cold-test behavior: 0 is lower than 10, so 0W-20 flows more easily when cold. The numbers after the dash, 20 and 30, describe hot viscosity, which matters later once the engine warms.

• A: Higher numbers mean thicker oil in the matching test, so 10W flows less easily when cold.
• B: The number before the W differs between the two, so their cold behavior differs.
• C (correct): The winter number rates cold-test behavior, and the lower 0W rating flows better at a cold start.
• D: The 30 rates viscosity when hot, not at a cold start, so it does not answer the cold-flow question.

Answer: B

Correct answer: The metal could bridge a live terminal and ground and quickly heat red-hot. The battery and starter circuits can deliver hundreds of amperes with little or no fuse protection. A ring or watch band that touches positive and ground at the same time becomes a short, heating red-hot in seconds. That is why jewelry comes off and tools must never bridge the terminals.

• A: Vented hydrogen is a spark and flame hazard, but jewelry does not attract the gas.
• B (correct): High-current circuits can push hundreds of amperes through a ring or watch band, heating it enough to burn skin within seconds.
• C: The danger is a short circuit through the metal, not a meter reading error.
• D: Acid is a skin and eye hazard, but it does not dissolve jewelry almost instantly; the key danger from jewelry is the short circuit.

Answer: B

Correct answer: A bump under one wheel tugs more on the other side, making the ride harsher. An anti-roll bar twists when one side compresses more than the other. A thicker bar resists that difference more, cutting lean, but it also ties the two sides together, so a bump under one wheel affects the other and the ride can feel harsher.

• A: An anti-roll bar does not replace dampers; spring motion over rough pavement still has to be damped.
• B (correct): A thicker bar couples left and right more tightly, so one-wheel bumps are passed across and wheels act less independently.
• C: Ride height is set by the springs; the bar does not lift the body and does little when both sides move together.
• D: Free play comes from worn joints and loose mounts in the steering linkage, not bar thickness.

Answer: A

Correct answer: 50 cc. Write the ratio and solve for the clearance volume.

That means

cc. Check: (475 + 50) divided by 50 is 10.5.

• A (correct): The total volume is 10.5 times the clearance, and the swept volume is the other 9.5 parts, so 475 divided by 9.5 gives 50 cc.
• B: This divides the swept volume by 10.5, treating 475 cc as if it were the total volume and leaving clearance out.
• C: This is the total volume at BDC, 475 plus 50 cc; the question asks for the clearance volume alone.
• D: This divides by 8.5, subtracting 2 from the ratio instead of 1.

Answer: C

Correct answer: 147 ft. Braking distance is proportional to the square of speed. The speed ratio is

• A: This scales distance in direct proportion to speed, but braking distance grows with the square of speed.
• B: This simply doubles the distance; the speed ratio is 1.75, and its square, not 2, sets the new distance.
• C (correct): The speed ratio is 70/40 = 1.75, and 1.75 squared is about 3.06, so 48 ft times 3.0625 is 147 ft.
• D: This applies the four-times rule for doubled speed, but 70 mph is not double 40 mph.