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Inelastic Collisions

Inelastic Collisions. Energy Loss. Friction can cause a loss of energy at contact. Real springs are not perfectly elastic Materials heat up The energy not lost at the collision is available for kinetic energy. Inelastic collisions always have a loss of kinetic energy.

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Inelastic Collisions

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  1. Inelastic Collisions

  2. Energy Loss • Friction can cause a loss of energy at contact. • Real springs are not perfectly elastic • Materials heat up • The energy not lost at the collision is available for kinetic energy. • Inelastic collisions always have a loss of kinetic energy.

  3. A 950 kg car sits at the bottom of an icy hill. It is struck by a 7600 kg truck moving at 50 km/h. If they stick together, how far do they move uphill? Momentum is conserved. The initial momentum is only P = m2v2 The final momentum is P = (m1 + m2) vf = Mvf The final velocity is vf = m2v2 / M = 44 km/h Energy is conserved uphill. Mgh = (1/2) Mvf2 h = vf2 / 2g = 7.8 m Stuck Together v2i h m2 m1

  4. Completely Inelastic • Collisions that end with the two objects together are completely (or perfectly) inelastic. • The energy lost in the completely inelastic collision is usually turned into heat. velocity after collision energy lost as heat

  5. Elasticity • Real collisions are generally not elastic. • Objects are deformed • Objects heat up • Kinetic energy not conserved • If there is some rebound, then there is elasticity. • Imperfect spring

  6. Coefficient of Restitution • In an elastic collision the initial and final velocities were exactly related. • For an inelastic collision the coefficient of restitution measures the relative amount of energy loss.

  7. Soft Ball • A ball rebounds to 70% of its initial height. What is the coefficient of restitution? v1f m1 v1i next

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