Lesson 29
Elastic and Inelastic Collisions

Name:faculty Section:M2 Start Time:12:15:53 Instructor:pate Course:355

1) Consider a perfectly elastic two dimensional collision between two Acme billiard balls. What's the best kind of collision if you want m1 (the black ball) to keep as much of its initial kinetic energy as possible? That is, how would that collision look? (Initially, would the red ball be moving toward the black one? Moving away from the black one? At rest? What about after the collision? How would it look?) Please briefly explain.

How, if at all, would your answer change if the balls had unequal masses?



2) Consider a head-on (1-d) collision between two shuffleboard rocks. (Yes, those 'puck things' are called 'rocks' in shuffleboard.) As with all real-world collisions, a collision between two such rocks is not perfectly elastic.

Suppose the blue shuffleboard rock collides with the red shuffleboard rock which is initially at rest. Also suppose the shuffleboard table surface is made by Acme (no friction). Estimate the fraction of kinetic energy retained by the rock system. E.g., estimate Tfinal/Tinitial. Please explain how you arrive at your estimate. (Hint: You'll probably want to consider the coefficient of restitution!)



3) Consider an automobile collision that brings to rest a motorist who was initially traveling at 65 mph. If the motorist's car is equipped with an airbag that deploys,

  1. the impulse of the collision is less than it would have been if the car hadn't been equipped with an airbag.
  2. the impulse of the collision is the same as it would have been if the car hadn't been equipped with an airbag.
  3. the impulse of the collision is more than it would have been if the car hadn't been equipped with an airbag.
  4. the relationship of the impulse with and without the airbag depends on the properties of the airbag, so cannot be specified.



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