Final answer:
The question involves understanding the tension in a cable, which is consistent throughout its length and is an example of Newton's third law. A force exerted by a cable is always parallel to its length and impacts the objects attached to its ends.
Step-by-step explanation:
The student's question pertains to the concept of tension in a cable, specifically cable CD with a tension (T) of 400 lb. Tension refers to the force exerted by a cable, rope, or any perfectly flexible connector that does not require force to bend. According to Newton's third law, the tension in the cable is the same throughout its length and the force that the cable exerts must be parallel to the length of the cable. Thus, the tension force at one point on the cable is reflective of the tension throughout the entire length of the cable. Moreover, the cable exerts equal and opposite forces on the objects it is connected to.
It is crucial to note that the force exerted by the cable is transmitted along the axis of the cable and this force is exerted on whatever is attached to both ends of the cable, be it a hand, a mass, or any other object. Hence, determining the tension at one location within a cable provides the value of tension at all locations along the cable.
When constructing problems involving tension, such as the tension in an elevator cable during acceleration, a free-body diagram is often utilized to visually represent the forces acting upon the system of interest. To calculate the tension in such a scenario, one would consider factors including the mass of the elevator and its load, the final velocity, and the time taken to reach that velocity.