Aim: How do we use conservation of momentum to analyze collisions?

Conservation of Momentum If momentum is conserved in a collision, this means that the total momentum of the system before the collision is equal to the total momentum of the system after the collision. Pbefore = pafter

Perfectly Inelastic Collision A collision in which kinetic energy is not conserved. A perfectly inelastic collision is a collision in which two objects collide and stick together, thus the maximum possible fraction of kinetic energy is transformed.

Thought question A skater is using very low friction rollerblades. A friend throws a frisbee at her, along the the straight line along which she is skating. Describe each of the following events as elastic, an inelastic, or a perfectly inelastic. She catches the Frisbee and holds it. She tries to catch the Frisbee but it bounces off her hands and falls to the ground at her feet. She catches the Frisbee and immediately throws it back with the same speed (relative to the ground) to her friend. A- Perfectly Inelastic Collision B- Inelastic Collision C- Elastic Collision

Inelastic collision Inelastic Collision m1v1i +m2v2i = (m1 + m2)vf

Thought Question In a perfectly inelastic collision between two identical objects, under what conditions is all of the initial kinetic energy of the system of two objects transformed to other forms of energy? If both objects have equal and opposite momenta, they will stick together and come to rest.

Carry collision insurance-Problem 1 An 1800 kg car stopped at a traffic light is struck from the rear by a 900 kg car and the two become entangled. If the smaller car was moving at 20.0m/s before the collision, what is the speed of the entangled cars after the collision?

Perfectly inelastic-Problem 2 A 2.50 kg object, moving initially with a speed of 10.0 m/s makes a perfectly inelastic head- on collision with a 5.00 kg object that is initially at rest. Find the final speed of the composite object. How much of the system kinetic energy is transformed to other forms during the collision? a) 3.33m/s b) 83.4 J

Problem 3 A railroad car of mass 2.50 x 104 kg is moving with a speed of 4.00 m/s. It collides and couples with three other coupled railroad cars, each of the same mass as the single car and moving in the same direction with an initial speed of 2.00 m/s. What is the speed of the four cars after the collision? How much mechanical energy is lost in the collision? 2.50 m/s, -37.5kJ

Problem 4 A 12 g wad of sticky clay is hurled horizontally at a 100 g wooden block initially at rest on a horizontal surface. The clay sticks to the block. After the impact, the block slides 7.50 m before coming to rest. If the coefficient of friction between the block and the surface is 0.650, what was the speed of the clay immediately before impact? 91.2 m/s