SIMULATION
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The law of conservation of momentum is a powerful generalization of Newton’s third law. For an isolated system, the total momentum of all the objects inside is constant. In this investigation, you will explore the conservation of momentum for two carts that are subject to no outside net force. The only catch is that the carts have a compressed spring inserted between them! Is momentum conserved for this system?
Part 1: Conservation of momentum for spring-loaded carts
1.
Select a mass for each cart.
2.
Press [Run] to start the simulation.
3.
Run the simulation for different combinations of masses for the two carts. Use your data table to record the mass and velocity for each combination.
1

Table 1: Velocity after the perfectly inelastic collision
Initial velocity of incident ball m
1
: __2 m/s____ Initial velocity of target ball m
2
: 0 m/s m a
s
s
m
1
Red target ball, mass m
2
5 kg 10 kg 20 kg
5 kg
10 kg
20 kg
50 kg
50 kg 100 kg
100 kg
Questions USE Phrases / Words SUCH AS – “HALF, More than Half, Less than Half” a.
Describe the velocities before and after the collision when masses are equal. b.
Describe the velocities (before and after) when the red target ball has more mass. c.
Describe the velocities (before and after) when the green ball has more mass. d.
As a result of the collision, does the total momentum of the system increase, decrease, or remain the same? Does the total kinetic energy of the system increase, decrease, or remain the same?
2

Applying new knowledge: Assume all collisions are one-dimensional.
1.
A 10 kg puck initially moving at 20 m/s has a perfectly inelastic collision with a 20 kg puck. a.
Will the resulting velocity be greater than, less than, or equal to 10 m/s? b.
Calculate the resulting velocity.
2.
A 2000 kg car traveling at 8.0 m/s has a rear-end collision with a 1500 kg car stopped at a traffic light. The cars lock bumpers and skid off together. a.
Which of the ranges below is correct for the resulting velocity?
A. 0 m/s < v < 4 m/s B. 4 m/s < v < 8 m/s C. 8 m/s < v < 12 m/s b.
Calculate the resulting velocity.
3.
Two 10 kg pucks head straight towards each other with velocities of 10 m/s and -20 m/s.
They collide and stick together. Calculate the resulting velocity.
PLUNGER CARTS
Procedure:
1. Using one cart with a retractable "plunger" and another cart without a plunger, place the two carts on the track between the two photogates. Push the retractable plunger into the plunger cart so that it locks and does not pop out. Place the plunger end of the plunger cart up against the other cart so that when you tap the peg on the top of the plunger cart, the spring-loaded plunger pops out and pushes the two carts apart, each passing through a photogate, as seen in figure 1.
2. When you are ready to collect data, click on the Collect button on the toolbar and lightly tap the peg on the top of the plunger cart so that the spring-loaded plunger pops out and pushes the two carts apart causing each cart to pass through a photogate.
3. Record the velocity of the carts in the data table for recoil on your student answer page for the time just after they recoil away from each other.
4. Repeat the experiment for several more runs, adding various amount of mass to each cart to see how the amount of mass affects the velocity and momentum of the carts before and after the collision. Remember to record the data in such a way that another lab group can understand how you have organized your data and use it to answer questions about your data
3

1
2
3
4
5
DATA AND OBSERVATIONS
Mass of one empty cart: 0.500 kg
Fill in the data tables on the next page and answer the questions
Table 1
Run
1
2
3
4
5
Mass of
Incident
Car, m
(kg)
1
Mass of
Target
Cart, m
(kg)
2
Velocity v
1 of m
1
Before
Collision,
(m/s)
Table 2
Run
Momentum p
1
of m
1 before collision
(kg m/s)
Momentum p
2
of m
2 before collision
(kg m/s)
0
0
0
0
0
Total
Momentum of System
Before
Collision
Velocity v
2 of m
2
Before
Collision
0
0
0
0
0
Momentum p
1 of m
1 after collision
(kg m/s)
Velocity v
1f
of
After
Collision,
(m/s) m
1
Momentum p
2 of m
2 after collision
(kg m/s)
Velocity v
2f
of m
After
2
Collision,
(m/s)
1. In general, does the data collected for the recoil of the two carts seem to verify the law of conservation of momentum? Explain your answer and indicate which run of the recoil of the two carts best conserves momentum.
Sim = Simulatoin Plu = Plunger Carts
Section Sim A Sim B Sim C Sim D AKN 1 AKN 2 AKN 2 Plu Table 2 Plu #1
Points 5 5 5 5 5 5 5 5 10
Total
Momentum of System
After
Collision
4