#### Transcript Chapter 9 Momentum - Mrs. Krusa`s Wikispace

Chapter 9 Momentum Is equal to the mass of an object times the velocity of an object Has the symbol “p” so p= m • v - measured in kg•m/s - It is a vector quantity Momentum and Impulse Connection F=m a= m (v/t) F= m (v/t) Ft= m v Impulse= change in momentum or Impulse= pf-pi Con. Impulse(J)= F•t= m•v This is known as the impulse-momentum change equation 3 Major Truths 1. The impulse experienced by an object is the force • time. 2. The momentum change of an object is the mass•velocity change. 3. The impulse equals the momentum change. http://www.glenbrook.k12.il.us/gbssci/phys/Cla Example A 2200-kg car traveling at 26 m/s can be stopped in 21 s by gently applying the brakes. It can be stopped in 3.8 s if the driver slams on the brakes, or in .22 s if it hits a concrete wall. What average force is exerted on the car in each of these stops? Videos of Safety built into Cars http://www.youtube.com/watch?v=kzq PwrvOwYI Law of Conservation of Momentum The momentum of any closed, isolated system does not change pi = p f Two Particle Inelastic Collision A 1875kg Escalade going 23 m/s rear-ends a 1025 kg Cobalt going 17 m/s on ice in the same direction. The two cars stick together. How fast do the two cars move together immediately after the collision? Inelastic collision- two colliding objects stick together and move with the same final velocity Elastic collision- two colliding objects bounce off each other Example of Recoil Luke was studying his Physics while at practice. As he was standing in the middle of the rink, he decides to throw his book at Erik as he is skating by. He was totally amazed at the Physics law he just demonstrated. If the mass of the book is 2 kg and Luke’s mass is 77 kg, what is Luke’s velocity after he throws the book at 2 m/s? How long does it take Luke to reach the edge of the rink if the diameter of the rink is 10 meters? Example of Propulsion in Space An astronaut at rest in space fires a thruster pistol that expels 35 g of hot gas at 875 m/s. The combined mass of the astronaut and pistol is 84 kg. How fast and in what direction is the astronaut moving after firing the pistol? Examples of Two-Dimensional Collisions Example #1 A 1325 kg Cavalier moving north at 27.0 m/s, collides with a 2165 kg Lincoln moving east at 11.0 m/s. The two cars are stuck together. In what direction and with what speed do they move after the collision? Example # 2 A stationary billiard ball, with a mass of 0.17 kg, is struck by an identical ball moving at 4.0 m/s. After the collision, the second ball moves 60.0° to the left of its original direction. The stationary ball moves 30.0° to the right of the moving ball/s original direction. What is the velocity of each ball after the collision?