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0593_C10_fm Page 344 Monday, May 6, 2002 2:57 PM

344 Dynamics of Mechanical Systems

10.13 Closure
The work–energy principle is probably the most widely used of all the principles of
dynamics. The primary advantage of the work–energy principle is that it only requires
knowledge of velocities and not accelerations. Also, calculation of the work done is often
accomplished by inspection of the system configuration.
The major disadvantage of the work–energy principle is that only a single equation is
obtained. Hence, if there are several unknowns with a given mechanical system, at most
one of these can be obtained using the work–energy principle. This in turn means that
the principle is most advantageous for relatively simple mechanical systems. However,
the utility of the principle may often be enhanced by using it in tandem with other
dynamics principles — particularly impulse–momentum principles.
In the next two chapters we will consider more general energy methods. We will consider
the procedures of generalized dynamics, Lagrange’s equations, and Kane’s equations.
These procedures, while not as simple as those of the work–energy principle, have the
advantage of still being computationally efficient and of producing the same number of
equations as there are degrees of freedom of a system.

References (Accident Reconstruction)
10.1. Baker, J. S., Traffic Accident Investigation Manual, The Traffic Institute, Northwestern University,
Evanston, IL, 1975.
10.2. Backaitis, S. H., Ed., Reconstruction of Motor Vehicle Accidents: A Technical Compendium, Publi-
cation PT-34, Society of Automotive Engineers (SAE), Warrendale, PA, 1989.
10.3. Platt, F. N., The Traffic Accident Handbook, Hanrow Press, Columbia, MD, 1983.
10.4. Moffatt, E. A., and Moffatt, C. A., Eds., Highway Collision Reconstruction, American Society of
Mechanical Engineers, New York, 1980.
10.5. Gardner, J. D., and Moffatt, E. A., Eds., Highway Truck Collision Analysis, American Society of
Mechanical Engineers, New York, 1982.
10.6. Adler, U., Ed., Automotive Handbook, Robert Bosch, Stuttgart, Germany, 1986.
10.7. Collins, J. C., Accident Reconstruction, Charles C Thomas, Springfield, IL, 1979.
10.8. Limpert, R., Motor Vehicle Accident Reconstruction and Cause Analysis, The Michie Company,
Low Publishers, Charlottesville, VA, 1978.
10.9. Noon, R., Introduction to Forensic Engineering, CRC Press, Boca Raton, FL, 1992.

Problems

Sections 10.2 and 10.3 Work
P10.2.1: A particle P moves on a curve C defined by the parametric equations:

2
t
x = , y = t , z = t 3