Final answer:
The most probable cause of a negative final velocity in a deceleration problem is likely a calculation error. The required force each train engine needs to apply can be calculated using Newton’s second law considering the total mass of the train and the friction force. The force in the coupling between two cars is determined by the mass each coupling is pulling and the acceleration needed.
Step-by-step explanation:
The student’s question relates to the dynamics of a freight train and involves the understanding of basic principles of physics concerning force, mass, and acceleration. The mention of a final velocity calculation error pertains to kinematics, a branch of mechanics. The probable cause for an incorrect calculation of final velocity, such as obtaining a negative velocity for a decelerating train, might arise from misuse of equations of motion or an arithmetic error, since velocity cannot be negative in this context.
For question 16, to find the force each engine must exert, Newton’s second law is used: F=ma. The total mass of the train m is the sum of the masses of the engines and cars. With the given acceleration a, total mass, and frictional force Ff, the required force F can be calculated using the equation: F = (ma) + Ff. The answer to part b, the force in the coupling, can be found by considering the mass that the coupling is pulling from the rest of the train, applying Newton's second law again.