**Truck Rear Ends Car**

**Inelastic Collision**

This animation depicts an inelastic collision between a truck and
a car. In the collision between the truck and the car, total system
momentum is conserved. Before the collision, the momentum of the
truck is 60000 kg*m/s and the momentum of the car is 0 kg*m/s; the
total system momentum is 60000 kg*m/s. After the collision, the
momentum of the truck is 45000 kg*m/s and the momentum of the car is
15000 kg*m/s; the total system momentum is 60000 kg*m/s. Consistent
with the law of momentum conservation, the total system momentum is
conserved. The momentum lost by the truck (15000 kg*m/s) is gained by
the car.

An analysis of the kinetic energy of the two vehicles reveals that
the total system kinetic energy before the collision is 600000 Joules
(600000 J for the truck plus 0 J for the car). After the collision,
the total system kinetic energy is 450000 Joules (337500 J for the
truck and 112500 J for the car). The total kinetic energy before the
collision is __not__ equal to the total kinetic energy after the
collision. A portion of the kinetic energy is converted to other
forms of energy such as sound energy and thermal energy. A collision
in which total system kinetic energy is __not__ conserved is known
as an inelastic collision.

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