# Physics 102 Introduction to Physics

car crashes https://www.youtube.com/watch?v=4eCJ3rJ-w P0 EQ: How is momentum conserved when there is interaction between two objects in a closed system? Medicine ball collisions https://www.youtube.com/watch?v=W9EqU1_DXUw

Think Newtons 3rd Law in a collision The size of the force on the first object equals the size of the force on the second object. They are just

opposite in direction Forces always come in pairs - equal and opposite action-reaction force pairs. Newtons 3rd Law of Motion Collision

not observing unequal forces upon the ball and club head, but rather unequal accelerations Collision of unequal masses of equal masses each object experiences the

same acceleration. Forces cause acceleration, not motion For a collision occurring between object 1 and object 2 in an isolated system, the

total momentum of the two objects before the collision is equal to the total momentum of the two objects after the collision. That is, the momentum lost by object 1 is equal to the momentum gained by object 2.

This means that the momentum doesnt change. Isolated System An isolated system is a system that is free from the influence of a net external force that alters the momentum of the system

No system is completely isolated, there will always be a resistance force of some kind robbing the system of its momentum (air, friction) Momentum is conserved in any collision, elastic and inelastic. Momentum is conserved in recoil or propulsion Pi = m1v1i m2 v2Pi fm1v1 f m2 v2 f

Kangaroos are good runners that can sustain a speed of 56 km/h (15.5 m/s). Suppose a kangaroo is sitting on a log that is floating in a lake. When the kangaroo gets scared, she jumps off the log with a velocity of 15 m/s toward the bank. The log moves with a velocity of 3.8 m/s away from the bank. If the mass of the log is 250 kg, what is the mass of the kangaroo?

Conservation of momentum states that the total momentum of the two objects before the collision is equal to the total momentum of the two objects after the collision. How is this accomplished? Identify who experiences the greater force, impulse, momentum change, acceleration? Elastic collision: Particles bounce off each other without loss of energy.

Perfectly inelastic collision: After colliding, particles stick together and move with a common velocity after the collision. There is a loss of Kinetic Energy (sound, heat, deformation). Inelastic collision: Particles collide with some loss of energy, but dont stick together.

Hockey collisions: http:// science360.gov/obj/video/1a6a8602-2e8b-4eab-93e2-b6d 5a9e697ed/force-impulse-collisions 11 Momentum is conserved pi p f

m1v1i m2 v2i (m1 m2 )v f KE is transformed to other types of energy = Eloss K i K f Eloss 1 1 1 2 2 2 m1v1i m2 v2i (m1 m2 )v f Eloss

2 2 2 12 An arrow is fired into a small target at rest on a frictionless surface. The arrows mass is 20.0 g and the targets mass is 2.50 kg. If the speed of the arrow and target combined is 0.67 m/s, what is the arrows

initial speed? Momentum is conserved: collision is a An m Elastic 1v1i m2 v2 i m1v1 f m2 v2 f collision in which the Energy

is conserved : objects dont stick together 1 1 1 1 2 2 2 2 m1v1total

m2momentum v2i m1v1 f m so the and i 2 v2 f 2 2 2 2 the total kinetic energy remain constant. 17

In the game of marbles, a shooter is a large marble about 0.02 m in diameter that is used to knock smaller marbles out of the ring. Suppose a shooter with a speed of 0.80 m/s hits a 4.8x10-3 kg marble that is at rest in the ring. The shooter continues forward with a speed of 0.51 m/s while the smaller marble moves forward with a speed of 1.33 m/s. What is the mass of the shooter? o A large truck and a Volkswagen have a head-on collision. Which vehicle

experiences the greatest force of impact? (Remember Newtons 3 rd Law) o A large truck and a Volkswagen have a head-on collision. Which vehicle experiences the greatest impulse? (Remember Newtons 3rd Law) o A large truck and a Volkswagen have a head-on collision. Which vehicle experiences the greatest acceleration? (Remember Newtons 3 rd Law) o

Two objects stick together and move with a common velocity after colliding. Identify the type of collision https://www.flickr.com/photos/physicsclassroom/galleries/72157625280491634/ In a two body collision in an isolated system a.Kinetic energy is always conserved b.Momentum is always conserved c.Neither momentum not kinetic energy is

conserved d.Both momentum and kinetic energy are always conserved

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