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Ch 8 Momentum, Impulse, and Collisions © 2005 Pearson Education

8.1 Momentum and Impulse definition of momentum Newton’s second law in terms of momentum constant net force impulse-momentum theorem Definition of impulse © 2005 Pearson Education

Area = Impulse © 2005 Pearson Education

Example 8.3 A Soccer ball has a mass of 0.4kg. Initially, it is moving to the left at 20 m/s, but then it is kicked and given a velocity at 45° upward and to the right, with a magnitude of 30m/s. Find the impulse of the net force and the average net force. And Δt=0.01s A Soccer ball has a mass of 0.4kg. Initially, it is moving to the left at 20 m/s, but then it is kicked and given a velocity at 45° upward and to the right, with a magnitude of 30m/s. Find the impulse of the net force and the average net force. And Δt=0.01s © 2005 Pearson Education

ANS: Velocity components: X-component of impulse is equal to the x-component of momentum change, and the same is true for y-component © 2005 Pearson Education

The components of the average net force on the ball are The magnitude and direction of the average force are © 2005 Pearson Education

8.2 Conservation of Momentum © 2005 Pearson Education

Total momentum of a system of particles © 2005 Pearson Education

8.3 Inelastic Collisions © 2005 Pearson Education

Because after collision two bodies stick together. Therefore Conservation of momentum gives the relation The ratio of final to initial kinetic energy is © 2005 Pearson Education

Elastic Collisions © 2005 Pearson Education

For conservation of kinetic energy Conservation of momentum © 2005 Pearson Education

8.4 Elastic Collisions © 2005 Pearson Education

A and B have different mass In a straight-line elastic collision of two bodies, the relative velocities before and after the collision have the same magnitude but opposite sign © 2005 Pearson Education

8.5 Center of Mass Center of mass Body or collection of particles © 2005 Pearson Education

8.6 Rocket Propulsion © 2005 Pearson Education

Summary

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