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Unit 7 - Momentum, Impulse, and Collisions

Unit 7 - Momentum, Impulse, and Collisions. 7.1 Momentum and Impulse. Momentum is a vector quantity that is the product of an object’s mass and velocity Symbol is p (because we already use m for mass) Units are: The formula is:. Problems.

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Unit 7 - Momentum, Impulse, and Collisions

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  1. Unit 7 - Momentum, Impulse, and Collisions

  2. 7.1 Momentum and Impulse • Momentum is a vectorquantity that is the productof an object’s mass and velocity • Symbol is p (because we already use m for mass) • Units are: • The formula is:

  3. Problems • A 2250 kg truck has a velocity of 25 m/s to the east. What is the momentum of the truck? • What velocity must a car with a mass of 1210 kg have in order to have the same momentum as the truck?

  4. Impulse • Changing momentum takes force and time • Impulseis force multiplied by a time interval and expressed as F∆ t • Units are the same as for momentum: • The formula is:

  5. Impulse in Sports • "Follow Through" is important in many sports. • In baseball, follow through keeps the bat in contact with the baseball longer, making the ball go farther. • It makes the change in momentum greater

  6. Impulse Problems • A 1400 kg car moving westward at 15.0 m/s hits a pole. In 0.30 s it comes to a stop. What force was imparted on the car? • A 0.40 kg soccer ball moves to the north 18 m/s. After being kicked it moves 22 m/s to the south. What was the impulse delivered to the ball?

  7. 7.2 Conservation of Momentum • Momentum is conserved during collisions. • That means the total momentum beforea collision equals the total momentum after a collision. • Law of conservation of momentum:

  8. Explosions • Just like momentum is conserved in collisions, momentum is also conserved in an explosion.

  9. Collision/Explosion Problems • A 75.0 kg boater stands in a 45.0 kg boat initially at rest. The boater then steps out of the boat with a velocity of 2.5 m/s to the right. What is the final velocity of the boat? • You throw a .50 kg bocce ball. It hits your opponents .60 kg bocce ball with a velocity of 5.0 m/s and stops. What is the velocity of your opponents ball?

  10. 7.3 Types of Collisions • There are two fundamental types of collisions: • Elastic and Inelastic

  11. Inelastic Collisions • Inelastic collisions are when two objects hit and combine. • Examples: arrow and target, meteor and earth • Total momentum is conserved but kinetic energy is not.

  12. Elastic vs inelastic collisions

  13. Formula for inelastic collisions • because the two objects combine after the collision their masses are added together and they are treated as a single object.

  14. Elastic Collisions • Two objects collide and bounce off each other. • Examples: billiard balls, high fives • Total Momentum and kinetic energy are conserved.

  15. Formula for Elastic Collisions • Because the two objects bounce off each other they are treated as separate objects before and after the collision. • Note – this formula is the same formula as for the law of conservation of momentum!

  16. Collision Problems • A 0.25 kg arrow moving 12 m/s to the west pierces a 6.8 kg target. • What type of collision is this? • What is the final speed of the target and arrow? • What is the change in kinetic energy?

  17. Collision Problems • A 16.0 kg canoe is moving to the left at 12 m/s until it bounces off a 4.0 kg raft moving to the right at 6.0 m/s. After the collision the raft moves to the left at 22.7 m/s. • What type of collision is it? • What is the final velocity of the canoe? • What is the change in kinetic energy?

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