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Combination Vehicles Practice Question 39

Required for Class ACombination Vehicles · Question 39

The forward thrust between trailer and tractor on a hard stop is absorbed by:

• AThe kingpin and fifth wheel coupling
• BRear suspension only
• CTrailer brakes alone
• DThe driver's seat belt

Correct answer: A. The kingpin and fifth wheel coupling

Why: All longitudinal forces between trailer and tractor pass through the kingpin and fifth wheel. This is why fifth wheel inspection is critical.

How this question fits the Combination test

Articulated vehicles fail in unique ways: trailer swing under braking, rearward amplification under steering, and jackknife under loss of traction. Combination Vehicle knowledge is required for any Class A applicant under 49 CFR 383.111.

Study technique for this topic

Walk through the coupling sequence verbally until it's second nature. Know the safe-rolling rearward amplification factor, the difference between trailer service brakes and parking brakes, and what creates the conditions for a tractor jackknife.

Related Combination practice questions

• Q20. When checking trailer brakes via the hand valve, you should:
• Q33. When the trailer wheels lock during heavy braking, you should:
• Q47. When driving across railroad tracks with a low-clearance trailer (lowboy), you should:
• Q60. When making a tight backing maneuver, looking ahead in your mirrors to predict trailer mov…
• Q9. The coupling height check before backing under the trailer is critical because:

Continue your CDL preparation

The Combination Vehicles portion of the CDL knowledge exam covers more than this single question. Use this site's full Combination Vehicles bank to drill every topic, then test yourself with one of our state-specific practice sets to confirm you are ready for the actual DMV exam in your state. Always check your state's CDL handbook for any local addenda before the test day.

If you are still building your overall CDL foundation, start with the General Knowledge bank — every CDL applicant must pass it — and then work outward to the endorsements you plan to add.