Final answer:
The couch in the truck bed will most likely fall out when the truck accelerates, due to Newton's first law of motion as there's no restraining strap to overcome the couch's inertia.
Step-by-step explanation:
When the truck pulls away from the stop sign onto the busy highway, the most likely outcome for the couch with a broken strap is b) The couch will fall out of the truck bed. This is because, according to Newton's first law of motion, an object at rest tends to stay at rest unless acted upon by an external force. In this case, the truck is the object in motion, and the couch is the object at rest. As the truck accelerates, there is no longer sufficient force from the strap to counteract the couch's inertia; consequently, the couch is likely to stay behind as the truck moves forward, resulting in it falling out of the bed of the truck.
Another way to examine this scenario is through the concept of inertia and friction. With the strap broken, the friction between the couch and the truck bed might not be enough to overcome the couch's inertia if the truck accelerates rapidly. Lacking the additional restraining force that the strap would provide, the couch could slide and fall out due to its inertia.