Final answer:
The next step after the primary assessment of an unresponsive patient struck by a vehicle is to begin the secondary assessment.
Step-by-step explanation:
The next step after completing the primary assessment of an unresponsive patient struck by a vehicle would be to begin the secondary assessment. The secondary assessment involves a systematic head-to-toe examination of the patient to identify any additional injuries that may not have been immediately apparent during the primary assessment. This includes assessing for secondary injuries such as fractures, head injuries, and internal bleeding.