UNIT 2 – ENERGY and MOMENTUM CHAPTER 5 – Momentum - 5.1 Momentum and Impulse o Momentum is the product of the mass of a moving object and its velocity p = mv where p is momentum of an object in kg m/s o the force applied and time to apply the force affect the momentum using Newton’s 2nd law o the net force on an object equals the rate of change of the objects momentum Ex. 1. A hockey puck with a mass of 0.83 kg is passed across the ice with a force of 16.3 N. Initially the puck has a speed of 18 m/s and a coefficient of kinetic friction of 0.4 a. Calculate kinetic friction b. Calculate net force c. Determine the initial momentum of the puck d. Determine the final velocity of the puck as it travels for 1.37 s - 5.2 Conservation of Momentum o Law of conservation of linear momentum If net force acting on a system of interacting objects is zero, then the linear momentum of the system before the interaction equals the linear momentum of the system after the interaction Ex. 1. You hit the white ball with a speed of 4.6 m/s against a somewhat stationary 8 ball that then travels with a speed of 3.2 m/s. After the collision the white ball travels with a speed of 1.4 m/s in the opposite direction and all the balls have an approximate mass of 2.2 kg. Determine the initial speed of the 8 ball. - 5.3 Elastic and Inelastic Collisions o Elastic collision – the total K.E. after the collision equals the total K.E. before the collision Almost impossible to occur because after collision some energy is always lost to surroundings o Inelastic collisions – the total K.E. after is different from the total K.E. before the collision o Complete inelastic collision – there is a max decrease in K.E. after collision since objects stick together and move at the same velocity Usually the final K.E. is less then initial K.E. unless collision is explosive The decrease in K.E. is due to transfer of energy o Ex. To thermal (heat) energy As K.E. decreases, elastic P.E. increase For inelastic collisions i.e. conservation of momentum For complete inelastic collisions For elastic collisions Ex. 1. A truck of mass 1.3 x 104 kg travelling at 90 km/h [N], collides with a car of mass 1100 kg travelling at 30 km/h [N]. If the collision is completely inelastic, what are the velocities of the vehicles after the collision?