Car Rear Ends Truck

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 car is 20000 kg*m/s and the momentum of the truck is 0 kg*m/s. The total system momentum is 20000 kg*m/s. After the collision, the momentum of the car is 5000 kg*m/s and the momentum of the truck is 15000 kg*m/s. The total system momentum is 20000 kg*m/s. Consistent with the law of conservation of momentum, the total system momentum is conserved. The momentum lost by the car (15000 kg*m/s) is gained by the truck.

An analysis of the kinetic energy of the two vehicles reveals that the total system kinetic energy before the collision is 200000 Joules (200000 J for the car plus 0 J for the truck). After the collision, the total system kinetic energy is 50000 Joules (12500 J for the car and 37500 J for the truck). 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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For more information on momentum concepts and principles, visit The Physics Classroom Tutorial. Detailed information is available there on the following topics:

Momentum

Momentum Conservation Principle

Isolated Systems

Momentum Conservation in Collisions

Kinetic Energy