Transcript Collisions
Momentum and Collisions Banging things around… Momentum Impact or product of mass and velocity Represented by the variable “r” Formula r=mv Units are kg m/s •More mass means more impact has more impact – rolling a pingpong ball or bowling ball? •What •More speed means more impact • what has more impact -catching a tossed ball or line drive? MOMENTUM IS MASS TIMES VELOCITY Impulse The change in momentum Determined by the amount of force for how long Formula is Dp= Ft Classic example is seatbelt vs dashboard. Seatbelt means slower stop or less force Dashboard means faster stop or more force Newton’s Laws of Motion Change in momentum occurs when force is applied. 2nd For every force applied to an object, it applies each force back. 3rd Conservation of Momentum Momentum cannot be created or destroyed The results of any collision will not change the system momentum Two objects pushing off each other will have the same total momentum as before the action Collisions Three types of collisions Explosions Inelastic collisions Elastic collisions Momentum is always conserved Explosions Explosions are collisions where the objects begin as one and then separate into many objects traveling in different directions. All collisions begin with determining the masses involved in the collision. We designate these as m1 and m2. In an explosion, these two masses are added together before the explosion. And counted separately after the explosions. After the Explosion… The sum of the momentums after the explosion must equal the sum of the momentums before the explosion. (m1 + m2)v = m1v1 + m2v2 Don’t forget positive and negative directions. Example #1 A 40-kg boy is sitting on a frozen pond holding a 4-kg book. The ice is very slick and he cannot get off the ice. If he throws the book at 6 m/s. How fast will he travel in the opposite direction? M1 = 40 kg M2 = 4 kg MT = 44 kg V2 = 6 m/s vT = 0 m/s (m1 + m2)vT = m1v1 + m2v2 Inelastic collisions Objects collide and continue as one object – joined like two trains hooked together or a receiver catching a football. Formula is m1v1 + m2v2 = (mT)vT Example #2 Sante throws a 20-kg medicine ball at 10 m/s to his friend Frankie weighing a hefty 100 kgs who is moving away from Sante at 2 m/s. Somehow, Santee catches the ball and falls forward. What speed does he fall forward? M1 = 20 kg M2 = 100 kg MT = 120 kg V1= 10 m/s V2 = 2 m/s vT = ? m/s Elastic collisions Objects collide and then bounce off each other. Formula is: m1v1 + m2v2 = m1v1’ + m2v2’ Example #3 Two 200 kg bumper cars race towards each other at 10 m/s and 15 m/s. After the bump, the slower car moves away at a velocity of 12 m/s. What is the velocity of the faster car? m1 = 200 kg m2 = 200 kg V1 = 10 m/s v2 = -15 m/s V1’ =