Chapter 7 Linear Momentum

Chapter Momentum Linear Momentum- product of mass times velocity p=mvp=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 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 m 1 v i1 + m 2 v i2 = m 1 v f1 + m 2 v f2 rocket propulsion - initial momentum = 0 final total momentum = p gas + p rocket =0 (same magnitude opposite directions) pg. 184 Ex. 7-3, 7-4

Chapter Conservation of Momentum in collisions elastic collision - total kinetic energy is conserved total initial KE = total final KE 1/2 m 1 v i /2m 2 v i2 2 = 1/2 m 1 v f /2 m 2 v f2 2 inelastic collision - kinetic energy is not conserved, often changed to thermal energy

Chapter Solving Problems Conservation of momentum Momentum before = momentum after m 1 v i1 + m 2 v i2 = m 1 v f1 + m 2 v f2 Conservation of kinetic energy (elastic collision) Total KE initial = total KE final 1/2 m 1 v i /2 m 2 v i2 2 = 1/2 m 1 v f /2 m 2 v f2 2 V 1 -V 2 = V 2 ’-V 1 ’ = -(V 1 ’ -V 2 ’)

Chapter 7 –Write two equations –Cancel zero terms –Plug in known variables –Solve for unknown variable

Chapter 7 v i1 - v i2 = v f2 - v f1 = - (v f1 - v f2 ) 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