Chapter 8

# Chapter 8 - Collisions and Momentum Chapter 8 Momentum A...

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1 Chapter 8: Momentum A simple way to understand what happens in a collision is to use a quantity called momentum . We’ll find that the total momentum of a system is conserved if no external forces act on the system Collisions and Momentum An 18-wheeler moving at 30mph collides with a Honda Civic moving at 30mph - who comes off worse? Why? We intuitively know the Civic is in trouble and the reason is that it has much less mass. Which is more dangerous - a bullet moving at 1mph or one moving at 50mph? It is clear that both mass and velocity are important in these circumstances, so we define a quantity that includes both, momentum, (18 wheeler has more momentum, faster bullet has more momentum) Momentum and Newton’s 2 nd Law recall the mathematical formulation of Newton’s 2 nd law and recall that the acceleration vector was defined as the instantaneous change in the velocity vector if the mass is constant with time then so forces actually cause changes in momentum and this even works when the mass changes with time (an example would be rocket propulsion) Total momentum if we have a system of particles, the total momentum of the system is simply the vector sum of the momenta of the particles Example 8.1 - Preliminary analysis of a collision A compact car with a mass of 1000kg is traveling north at speed 15m/s when it collides with a truck of mass 2000kg traveling east at 10m/s. Treating each vehicle as a particle, find the total momentum just before the collision.

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2 Conservation of momentum Last time we learned of an example of a conservation law. We found that provided no external forces acted on a system to do work, the total energy in the system was conserved. With momentum we have another conservation law:
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Chapter 8 - Collisions and Momentum Chapter 8 Momentum A...

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