
257Accident Reconstruction
increases; if negative, it decreases. In the special case in which the only force on the body is
the gravitational force, the work W
P
is zero. en
1
1
2
2
21
2
1
mv mgym
gy+= +
(9.80)
Elastic Potential Energy
Another concept that is utilized in accident reconstruction is that of elastic potential
energy. is principle is introduced in the modeling of the crush deformation of a vehicle
during a collision and is based on Hooke’s law, which states that the elastic force is propor-
tional to the displacement of the spring. Consider Figure 9.14.
When an external force P stretches or compresses the spring so as not to permanently ...