## Due 3:30 pm, Thursday, October 8th

Physics 105, Fall Term, 2009

Did you complete the reading assignment?

Yes
No

## KEY CONCEPTS:

1) Momentum of objects within a system are conserved through a collision.

2) Elastic collisions are collisions in which the objects bounce off of each other after colliding.

3) Inelastic collisions are collisions in which the objects stick together after colliding.

## Exercise 1

The following applet is not flashy, but it shows very simply how the conservation of momentum works in collisions: http://www.physics.upenn.edu/courses/gladney/phys1/lectures/lecture7/momentum_conservation.html

This applet is really self explanatory, just hit the 'Start' button to see a collision with the settings you are at and the 'Reset' button to put the objects back in place. You will see green words and numbers flashing right under the point of collision as the applet runs, these numbers give the total momentum, speeds, and kinetic energy of the collisions.

With the elasticity set to 100% and the masses and speeds set to 1, watch the collision. What do you see?

Is momentum conserved?

Yes
No

Is kinetic energy conserved?

Yes
No

Now change mass 1 to 5 and the speed of mass 1 to 3 and watch the collision. What do you see?

Is momentum conserved?

Yes
No

Is kinetic energy conserved?

Yes
No

Now change mass 1 to 1 and the speed of mass 1 to 0 and watch the collision. What do you see?

Is momentum conserved?

Yes
No

Is kinetic energy conserved?

Yes
No

Now change the speed of mass 1 back to 1 and change the elasticity to 0% and watch the collision. What do you see?

Is momentum conserved?

Yes
No

Is kinetic energy conserved?

Yes
No

Now change the elasticity to 50% and watch to collision. What do you see?

Is momentum conserved?

Yes
No

Is kinetic energy conserved?

Yes
No

Under what condition is momentum in a collision conserved?

Under what condition is the kinetic energy of a collision conserved?

## Exercise 2

Sometimes it is forgotten that explosions and fuel propulsion are just special cases of collisions and the Law of Conservation of Energy. Watch the following video: http://www.youtube.com/watch?v=nNyzwnQ2Qe8

In this situation, what is the initial mass?

Mass of water in bottles
Mass of man
Mass of water in bottles and mass of man combined
Mass of water vapor exiting the bottle

What is the initial velocity?

Velocity of water in bottles
Velocity of man
Velocity of water in bottles and man combined
Velocity of water vapor exiting the bottle

What is the final mass?

Mass of water in bottles
Mass of man
Mass of water in bottles and mass of man combined
Mass of air exiting the bottle

What is the final velocity?

Velocity of water in bottles
Velocity of man
Velocity of water in bottles and man combined
Velocity of air exiting the bottle

What type of collision is this?

Elastic
Inelastic

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Was there anything that you didn't understand in the reading assignment?  What was confusing to you?