Honors Physics

Who can tip over the water jars of the heavens when the dust becomes hard and the clods of earth stick together.? Job 38:38

A situation where the objects “STICK” together. Notice you have TWO objects BEFORE, but ONE object AFTER the collision. Momentum is conserved, but Kinetic Energy is not.

Since KINETIC ENERGY was NOT conserved during the collision we call this an INELASTIC COLLISION.

Two boxcars are being assembled at a switching yard. Car 1 has a mass of 6.5 x 10 3 kg and moves with a velocity of m/s. Car 2 has a mass of 9.2 x 10 3 kg and a velocity of m/s. Car 2 slams into Car 1 and they couple together. Find the final velocity of the cars after they couple together.

At an intersection, a 1500 kg car traveling east at 25 m/s collides with a 2500 kg van traveling north at 20 m/s. Find the direction and magnitude and direction of the velocity of the wreckage immediately after the collision, assuming that the vehicles undergo a perfect inelastic collision.

This type is often referred to as “backwards inelastic” (or recoil). Notice you have ONE object (we treat this as a SYSTEM) before the explosion and TWO objects after the explosion.

Suppose we have a 4-kg rifle loaded with a kg bullet. When the rifle is fired the bullet exits the barrel with a velocity of 300 m/s. How fast does the gun recoil backwards?

 Glancing Collisions ◦ Collisions do not always occur in a straight line.  Collision in 2 dimensions include variables such as angle and direction. ◦ Use vectors to break the velocities into x- and y-components.

Two shuffleboard disks of equal mass, are involved in a perfectly elastic glancing collision. The first disk, initially at rest, is struck by the second disk, moving to the right at 5.00 m/s. After the collision, the first disk makes an angle of 53° below the x-axis, while the second disk makes and angle of 37° above the x-axis. What is the velocity of each disk after the collision? Given: m 1 = m 2, v 1i = 0.00 m/s, v 2i = 5.00 m/s,  1 = -53 ,  2 = 37  Find: v 1f and v 2f

Sometimes objects stick together or blow apart. In this case, momentum is always conserved. When 2 objects collide and DON’T stick When 2 objects collide and stick together When 1 object breaks into 2 objects Elastic Collision = Kinetic Energy is Conserved Inelastic Collision = Kinetic Energy is NOT Conserved

1)List your given values and the values you need to find. 2)Set up a coordinate system and define velocities w.r.t this coordinate system. 3)Draw & label all velocity vectors & masses. 4)Write a general expression for the system momentum before & after the collision. 5)Fill in all known values. 6)If the collision is elastic, write the K.E. equation. 7)Solve the equations simultaneously.