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ELASTIC AND INELASTIC COLLISIONS

ELASTIC AND INELASTIC COLLISIONS. CH6 – Section 3. Section Objectives . Identify different types of collisions Determine the changes in kinetic energy during perfectly inelastic collisions

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ELASTIC AND INELASTIC COLLISIONS

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  1. ELASTIC AND INELASTIC COLLISIONS CH6 – Section 3

  2. Section Objectives • Identify different types of collisions • Determine the changes in kinetic energy during perfectly inelastic collisions • Compare conservation of momentum and conservation of kinetic energy in perfectly inelastic and elastic collisions • Find the final velocity of an object in perfectly inelastic and elastic collisions.

  3. Types of Collisions • Perfectly Inelastic Collision • A collision in which two objects stick together after colliding Example: meteorite colliding with earth • Elastic Collision • A collision in which two objects collide and then return to their original shape. Example: collision between billiard balls

  4. Perfectly Inelastic Collision(objects stick together after colliding) • Momentum is conserved in a Perfectly Inelastic Collision • The formula for conservation of momentum can be simplified: m1v1i + m2v2i = (m1 + m2)vf • Kinetic Energy is NOT conserved in a Perfectly Inelastic Collision (some KE is converted to sound energy and internal energy as the objects deform during the collision)

  5. Conceptual Challenge • A 0.75 kg clay ball moving at 3.8 m/s to the right strikes an identical ball moving at 3.8 m/s to the left. The balls stick together after the collision and stop. What percentage of the initial kinetic energy is converted to other forms?

  6. Elastic Collisions(objects do not stick together after colliding) • Total Momentum and Total Kinetic Energy are both conserved in Elastic Collisions. Conservation of Momentum m1v1i + m2v2i = m1v1f + m2v2f Conservation of Kinetic Energy ½ m1v1i2 + ½ m2v2i2 = ½ m1v1f2+ ½ m2v2f2

  7. Things to remember • Momentum and velocity are both vector quantities (establish a sign convention) • Most real world collisions are neither elastic nor perfectly inelastic • Formulas: • p = mv • KE = ½mv2 • Impulse = Change in Momentum, which can be expressed by F∆t = ∆p

  8. White Board Physics Challenge • A 16 kg canoe moving to the left at 12.5 m/s makes an elastic head-on collision with a 14.0 kg raft moving to the right at 16.0 m/s. After the collision, the raft moves to the left at 14.4 m/s. (Disregard any effects of the water.) A. Find the velocity of the canoe after the collision. B. Verify your answer by calculating the total KE before and after the collision.

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