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Chapter 7 Linear Momentum. 7.1 Momentum. Linear Momentum- product of mass times velocity p=mv p=momentum units=kg.m/sec Restate Newton’s second law - The rate of change of momentum of a body is equal to the net force applied to it F= p/ t pg. 182 Ex. 7-1. 7.2 Conservation of Momentum.
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7.1 Momentum • Linear Momentum- product of mass times velocity • p=mv p=momentum units=kg.m/sec • Restate Newton’s second law - The rate of change of momentum of a body is equal to the net force applied to it • F=p/t • pg. 182 Ex. 7-1 Chapter 7
7.2 Conservation of Momentum • Law of Conservation of Momentum - The total momentum of an isolated system of bodies remains constant. • Isolated system - one in which the only forces present are those between the objects of the system. • Momentum before = momentum after Chapter 7
Conservation of Momentum • m1vi1 + m2vi2 = m1vf1 + m2vf2 • rocket propulsion - initial momentum = 0 • final total momentum = pgas + procket =0 (same magnitude opposite directions) • pg. 184 Ex. 7-3, 7-4 Chapter 7
7.4 Conservation of Momentum in collisions • elastic collision - total kinetic energy is conserved • total initial KE = total final KE • 1/2 m1vi12 + 1/2m2vi22= 1/2 m1vf12 + 1/2 m2vf22 • inelastic collision - kinetic energy is not conserved, often changed to thermal energy Chapter 7
7.5 Solving Problems • Conservation of momentum • Momentum before = momentum after • m1vi1 + m2vi2 = m1vf1 + m2vf2 • Conservation of kinetic energy (elastic collision) • Total KE initial = total KE final • 1/2 m1vi12 + 1/2 m2vi22= 1/2 m1vf12 + 1/2 m2vf22 • V1-V2 = V2’-V1’ = -(V1’ -V2’) Chapter 7
Write two equations • Cancel zero terms • Plug in known variables • Solve for unknown variable Chapter 7
vi1 - vi2 = vf2 - vf1= - (vf1 - vf2) • For any head-on elastic collision, the relative speed of the two particles after the collision has the same magnitude as before, but opposite direction. • pg. 189 Ex. 7-6 & 7-7 Chapter 7