
Concept explainers
(a)
Find the distance (x) required to bring the train to stop.
(a)

Answer to Problem 13.17P
The distance (x) required to bring the train to stop is
Explanation of Solution
Given information:
The initial speed of the train
The coefficient of kinetic friction
The weight of train A
The weight of train B
The weight of train C
Assume the acceleration due to gravity (g) is
Calculation:
Show the free body diagram of the train A, B and C with the forces as in Figure (1).
Convert the unit of initial velocity of trailer truck from
Calculate the force at A
Substitute 0.35 for
Calculate the force at B
Substitute 0.35 for
Calculate the force at C
Substitute 0.35 for
Calculate the total weight (W) using the relation:
Substitute
Calculate the mass of the truck (m) using the formula:
Substitute
Calculate the initial kinetic energy
Substitute
The final kinetic energy
Calculate work done
Substitute
Use work and energy principle which states that kinetic energy of the particle at a displaced point can be obtained by adding the initial kinetic energy and the work done on the particle during its displacement.
Find the distance (x) required to bring the train to stop:
Substitute
Therefore, the distance (x) required to bring the train to stop is
(b)
Find the force in each coupling.
(b)

Answer to Problem 13.17P
The force in coupling AB is
The force in coupling BC is
Explanation of Solution
Given information:
The initial speed of the train
The coefficient of kinetic friction
The weight of train A
The weight of train B
The weight of train C
Assume the acceleration due to gravity (g) is
Calculation:
Consider car A:
Show the free body diagram of the train A with the forces as in Figure (2).
Assume
Calculate the mass of the truck (m) using the formula:
Substitute
Calculate the initial kinetic energy
Substitute
The final kinetic energy
Calculate work done
Substitute
Use work and energy principle which states that kinetic energy of the particle at a displaced point can be obtained by adding the initial kinetic energy and the work done on the particle during its displacement.
The expression for the principle of work and energy is as follows;
Substitute
Consider car C:
Show the free body diagram of the train C with the forces as in Figure (3).
Calculate the mass of the truck (m) using the formula:
Substitute
Calculate the initial kinetic energy
Substitute
The final kinetic energy
Calculate work done
Substitute
Use work and energy principle which states that kinetic energy of the particle at a displaced point can be obtained by adding the initial kinetic energy and the work done on the particle during its displacement.
Find the force in coupling BC:
Substitute
Therefore, the forces in coupling AB and BC are
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Chapter 13 Solutions
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