### Collision: Elastic & Inelastic Conservation of Momentum

```Collision Course:
Elastic and Inelastic Collisions
Corina Bot, PhD (NJIT, C2PRISM)
Caroline Savio (ESHS, NPS)
Career Day
May 11th, 2010
Outline of Presentation
 Lesson Plan in Conjunction with Applet
 Conclusion and Questions
Concepts Behind Collision Course Applet
 Used to distinguish elastic and inelastic collisions
 Conservation of momentum
Elastic collision
Conservation of momentum
m 1 v1 i  m 2 v 2 i  m 1 v1 f  m 2 v 2 f
v1 i  v 2 i   v1 f  v 2 f

momentum before collision = momentum after collision
results before = results after
Inelastic collision
Conservation of momentum
m 1v1i  m 2 v 2 i  m 1  m 2   v f
momentum before collision = momentum after collision

results before = results after
Introduction to Collision Course Applet
 Designed by C2PRISM Fellow Corina Bot, PhD.
 Dr. Bot interviewed six Advanced Placement Physics students
at once via focus-group .
 Students really liked the idea of acquiring a
physics concept shaped as a game.
Features of Collision Course Applet
 Multiple choice question game
 Takes place in neutral setting
 Player chooses which car to drive
 Contains sound effects
 Visible damage in the cars after collisions
 Cartoon policeman assigns ticket at collision scene
 Player must distinguish whether collision was elastic or inelastic
 A correct answer -> policeman gives you points and your ticket is
void
 An incorrect answer -> policeman gives you a ticket and you lose
points
Specifics on Applet Creation
 Java applet developed by software engineer students
at NJIT
 Flash software/plug-in required
 PC and Mac OS Compatible
Outline of Presentation
 Lesson Plan in Conjunction with Applet
Lesson Plan in Conjunction with Applet
 Engagement and Assessment
 Ideally, students work independently on applet using
computers in lab classroom.


If there are not enough computers in classroom, work in pairs.
Or perform applet in computer lab instead of physics lab.
 Formative Check
 The applet consists of multiple choice questions that evaluate
the student’s understanding of types of collisions.
Lesson Plan in Conjunction with Applet
 Some practice problems
 Mario and Luigi on Bumper Cars
 The physics classroom
 http://www.physicsclassroom.com/Class/momentum/u4l2d.c
fm
Elastic collision
Input: m1 = 300 kg
m2 = 400 kg
v1i = 20 km/h
v2i = 0 km/h
Calculate: v1f =? v2f = ?
Momentum
is conserved!
Solution
m 1 v1 i  m 2 v 2 i  m 1 v1 f  m 2 v 2
v1 i  v 2 i   v1 f  v 2
f

Inputs: m1 = 300 kg
m2 = 400 kg
v1i = 20 km/h
v2i = 0 km/h
(1)
f
(2)
Substitute values given in problem into equation (1):
km
300 kg  20
 0  300 kg  v1 f  400 kg  v 2
h
6000 kg 
km
 300 kg  v1 f  400 kg  v 2
h
f
Calculate: v1f=? v2f = ?
f
(3)
Substitute values given in problem into equation (2):
km
20
h
v2
f
 0   v1 f  v 2
km
 v1 f  20
f

(4)
h
Substitute equation (4) in equation (3):
6000 kg 
km 

 300 kg  v1 f  400 kg   v1 f  20

h 

km
h
6000 kg 
km
 300 kg  v1 f  400 kg  v1 f  8000 kg 
h
 2000 kg 
km
h
v1 f 
v2
f
 700 kg  v1 f
 2000
km
700
h
 v1 f  20
km
h
  2 . 85
km
h
  2 . 85
km
h
 20
km
h
 17 . 14
km
h
km
h
Inelastic collision
Input: m1 = 300 kg
m2 = 400 kg
v1i = 20 km/h
v2i = 0 km/h
Calculate: vf = ?
Calculate: momentum before & after collision
Momentum
is conserved!
Solution
Inputs: m1 = 300 kg
m2 = 400 kg
v1i = 20 km/h
v2i = 0 km/h
m 1 v1 i  m 2 v 2 i   m 1  m 2   v f
300 kg  20
km
h
6000 kg 
km
6000 km
700
Calculate: vf=?
 700 kg  v f
h
vf 
 0  300 kg  400 kg   v f
 8 . 57
h
km
h
momentum before collision = momentum after collision
m 1 v1 i  m 2 v 2 i   m 1  m 2   v f
300 kg  20
km
h
6000 kg 
km
h
 0  300 kg  400 kg   8 . 57
 5999 kg 
km
h
km
h
Conclusions
 Many senses engaged in learning process
Group discussion with class
 Group instruction with visual demonstration
 Independent work on applet and on practice problems
 Paired work (optional)

 Students will qualitatively and quantitatively
distinguish elastic from inelastic collisions.
Questions?
Thank You!
```