Download Momentum, Energy and Collisions

Momentum, Energy and Collisions Scoring Sheet
Name _________________________________________________ Date___________ Hr. ____
1. Student answered preliminary questions and explained reasoning
_______ 4 pts
2. Mass of carts recorded correctly
_______ 2 pts
3. Velocity table recorded correctly
_______ 5 pts
4. Momentum table filled out and calculated correctly
_______ 7 pts
5. Kinetic energy table filled out and calculated correctly
_______ 7 pts
6. Explained ratio for conservation of momentum
_______ 1 pt
7. Explained ratio for conservation of KE
_______ 1 pt
8. Explained whether momentum is conserved in each of the
three types of collisions based on the ratio and lab uncertainties
_______ 5 pts
9. Explained whether kinetic energy is conserved in each of the
Three types of collisions based on the ratio and lab uncertainties
10. Student has classified the three types of collisions
_______ 5 pts
_______ 3 pts
Total
_______ 40 pts
Momentum, Energy and Collisions
Name ___________________________________ Date _________ Hr. ____
Introduction
For two interacting objects, if there is no net external force then we expect the total momentum of
the system to be conserved. In contrast, energy is only conserved when certain types of forces
are exerted between the objects.
Collisions are classified as elastic (kinetic energy is conserved), inelastic (kinetic energy is lost) or
completely inelastic (the objects stick together after collision). Sometimes collisions are described
as super-elastic, if kinetic energy is gained. In this activity you will test for conservation of
momentum and conservation of energy for different types of collisions.
Preliminary Questions
1. If two carts with magnetic bumpers are pushed together such that the carts interact by
repulsion of the magnetic fields surrounding the magnets, predict what sort of collision
(described above) would take place. Explain your reasoning!
_____________________________________________________________________
_____________________________________________________________________
2. If two carts with Velcro strips on their ends are pushed together, predict what sort of collision
(described above) would take place. Explain your reasoning!
_____________________________________________________________________
_____________________________________________________________________
Procedure
1. Place a motion detector at each end of the track. Connect them to DIG/SONIC 1 and
DIG/SONIC 2 channels of the interface.
2. Open the file “19 Momentum Energy Coll” from the Physics with Computers folder.
3. Measure the masses of the two carts and record them in the data table.
4. Place two carts at rest in the middle of the track. Click: zero – both sensors - ok
5. With the magnetic bumpers facing each other push one cart gently towards the other. (Cart
2 should initially be at rest before the collision. Make sure that the motion detectors are
tracking each cart throughout the whole motion. Adjust if necessary. Use statistics to
determine the initial and final velocity of each cart. Enter these values into the table. Repeat.
(record your answers as runs one and two in the data table)
6. With the Velcro bumpers facing each other push one cart gently towards the other. Use
statistics to determine the initial and final velocity of each cart. Enter these values into the
table. Repeat. (runs three and four)
7. With the magnetic bumpers facing the Velcro bumpers push one cart gently towards the
other. Use statistics to determine the initial and final velocity of each cart. Enter these values
into the table. Repeat. (runs five and six)
Data Table
Mass of cart 1 (kg)
Run
number
Run
number
Momentum
of cart 1
before
collision
(kg•m/s)
Velocity of
cart 2
before
collision
Velocity of
cart 1 after
collision
Velocity of
cart 2
after
collision
(m/s)
(m/s)
(m/s)
(m/s)
0
2
0
3
0
4
0
5
0
6
0
Momentum
of cart 2
before
collision
(kg•m/s)
0
2
0
3
0
4
0
5
0
6
0
KE of
cart 1
before
collision
(J)
Velocity of
cart 1
before
collision
1
1
Run
number
Mass of cart 2 (kg)
1
KE of
cart 2
before
collision
(J)
0
2
0
3
0
4
0
5
0
6
0
Momentum
of cart 1
after
collision
(kg•m/s)
Momentum
of cart 2
after
collision
(kg•m/s)
Total
momentum
before
collision
(kg•m/s)
Total
momentum
after
collision
(kg•m/s)
Ratio of
total
momentum
after/before
KE of
cart 1
after
collision
(J)
KE of
cart 2
after
collision
(J)
Total KE
before
collision
(J)
Total KE
after
collision
(J)
Ratio of
total KE
after/before
Analysis
1. Determine the momentum (mv) of each cart before the collision, after the collision, and the
total momentum before and after the collision. Calculate the ratio of the total momentum after
the collision to the total momentum before the collision. Enter the values in your data table.
Show example calculations for one row on a separate sheet of paper.
2
2. Determine the kinetic energy (½ mv ) for each cart before and after the collision. Calculate
the ratio of the total kinetic energy after the collision to the total kinetic energy before the
collision. Enter the values in your data table. Show example calculations!
3. If the total momentum for a system is the same before and after the collision, we say that
momentum is conserved. If momentum were conserved, what would be the ratio of the total
momentum after the collision to the total momentum before the collision?
4. If the total kinetic energy for a system is the same before and after the collision, we say that
kinetic energy is conserved. If kinetic were conserved, what would be the ratio of the total
kinetic energy after the collision to the total kinetic energy before the collision?
5. For your six runs, inspect the momentum ratios. Even if momentum is conserved for a given
collision, the measured values may not be exactly the same before and after due to
measurement uncertainty. The ratio should be close to one, however. Is momentum
conserved in your collisions? Which type of collisions show conservation of momentum?
6. Repeat the preceding question for the case of kinetic energy. Is kinetic energy conserved in
the magnetic bumper collisions? How about the Velcro collisions? Is kinetic energy
consumed in the third type of collision studies? Classify the three collision types as elastic,
inelastic, or completely inelastic.