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Physics 1AL
CONSERVATION OF MOMENTUM
Summer Session II 2010
1
Introduction
You have a summer job at Amtrak with a group examining the crash between two trains. Your
supervisor wants you to calculate the results of two different cases.
The first is a perfectly inelastic
collision where the two trains stick to each other.
The other case is an elastic collision where the two
trains bounce of each other with no loss of kinetic energy. Since the trains may be carrying different
cargo, their masses may be different. Your supervisor wants you to calculate the final velocity of the
trains as a function of the masses and initial velocities of the trains. You decide to calculate the resulting
velocities for the system and then build a laboratory model using gliders to check your calculation.
Your Objective:
To experimentally determine the final velocities of two objects after collision.
______________________________________________________________________________
Prelab questions:
Read
sections 8.1, 8.2, 8.3 in Serway & Faughn
Answer
each of the following questions in a few sentences of your own words:
1.
Perfectly Inelastic Collision
.
Draw diagrams showing a situation where a bigger,
moving train,
v
i
, collides with a smaller train that is not moving.
Assume that after the
collision the trains stick together.
Show separate diagrams for the situation just before
the collision and just after the collision. Assume the trains have different masses (
m
big
and
m
small
).
Make sure you identify your isolated system.
Write down the momentum
conservation equation for the scenario in question.
Solve for the final velocity of the
two trains,
v
f
, in terms of
v
i
,
m
big
, and
m
small
.
2.
Elastic Collision
. Draw two diagrams for the situation where a moving train (with initial
speed
v
o
) collides elastically with a target train that is not initially moving, and the trains
use their springy bumpers to bounce off each other without damage. One diagram should
show the instant just before the collision and the other the instant just after the collision.
Assume the trains have different masses (
m
moving
and
m
target
) Make sure you identify your
isolated system
. Show that the final velocity of each train will be:
v
tar
get
=
2
v
o
1
+
m
tar
get
m
moving
"
#
$
$
%
'
'
v
moving
=
m
moving
"
m
tar
get
( )
m
moving
+
m
tar
get
( )
v
o
Hint: use conservation of momentum and the relation between the relative velocities
before and after collision that arises due to conservation of energy in section 8.3.
3.
A blue cart (mass = 0.400 kg) makes an elastic
collision with a red cart (mass = 0.750 kg). The
blue cart is initially moving at 1.40 m/s to the
right before the collision, and the red
cart is initially at rest.
What are the
final velocities of the blue and red carts (magnitude and direction)?
How much kinetic
energy is lost in the collision?
(Hint: refer to part C of this lab and prelab question 2)
4.
Make all the data tables you’ll need for experiments B & C ahead of time in your lab
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This note was uploaded on 09/25/2010 for the course PHYSICS 1A 1al taught by Professor Rafaelski during the Summer '10 term at UCSD.
 Summer '10
 Rafaelski

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