1Announcements1. HW5 due Feb 25.2. Prof. Reitze office hour this week: Friday 3 – 5 pm, (Wednesday 11-noon cancelled) 3. Midterm1: grades posted in e-learningsolutions and grade distribution posted on websiteif you want to look at your scantron, see Prof. Chan before March 3.4. Make-up exam: April 21, 7:30 pmcovers all material in the course.need to let Prof. Chan and Prof. Reitze know in advanceif you need to miss the midterms or final.location TBARecap: conservation of Momentum • The momentum of each object will change• The total momentum of the system remains constantRecap: Collisions• Momentum is conserved in any collision• Elastic collisions: kinetic energy is also conserved.• Inelastic collisions– Kinetic energy is not conserved• Some of the kinetic energy is converted into other types of energy such as heat, sound, work to permanently deform an object– Perfectly inelastic collisions occur when the objects stick together• Not all of the KE is necessarily lostTypes of Collisions• Elastic collision– both momentum and kinetic energy are conserved• Actual collisions– Most collisions fall between elastic and perfectly inelastic collisions73. A tennis ball of mass 57.0 g is held just above a basketball of mass 590 g. With their centers vertically aligned, both balls are released from rest at the same time, to fall through a distance of 1.20 m, as shown in Figure P6.69. (a) Find the magnitude of the downward velocity with which the basketball reaches the ground. (b) Assume that an elastic collision with the ground instantaneously reverses the velocity of the basketball while the tennis ball is still moving down. Next, the two balls meet in an elastic collision. (b) To what height does the tennis ball rebound?1.2 m 1.2 mvTvB21.2 m 1.2 mvTvB1.2 mvTvB'm1v1i + m2v2i= m1v1f+ m2v2fElastic collision: kinetic energy conservation(1/2)m1v1i2+ (1/2)m2v2i2= (1/2)m1v1f2+ (1/2)m2v2f2Momentum conservation:)vv(vvf2f1i2i1−−=−Only for 1 dimensional elastic collisionsv1i+ v1f = v2i+ v2forInelastic collisionsKinetic energy is not conservedMomentum is still conservedPerfectly Inelastic collisionsObjects stick together after collisionBallistic pendulum6.62 Two blocks of masses m1 = 2 kg and m2 = 4 kg are each released from rest at a height of 5 m on a frictionless track and undergo an elastic head-on collision. (a) Determine the velocity of each block just before the collision. (b) Determine the velocity of each block immediately after the collision. (c) Determine the maximum heights to which m1 and m2 rise after the collision.3airplanesneed AirRocket Propulsion• The operation of a rocket depends on the law of conservation of momentum as applied to a system, where the system is the rocket plus its ejected fuel– This is different than propulsion on the earth where two objects exert forces on each other• Road on car• Train on trackRocket Propulsion, 2• The rocket is accelerated as a result of the thrust of the exhaust gases• This represents the inverse of an inelastic collision– Momentum is conserved– Kinetic Energy is increased (at the expense of the stored energy of the rocket fuel)Rocket