Conservation of Momentum in One Dimension
Studio Physics I
Part I - Conservation of Momentum in One Dimensional Collisions
In this activity, we will use the concept of conservation of momentum to make
predictions about what happens in collisions between low friction carts moving on a
track. For each of the cases shown below, use the idea of conservation of momentum to
predict the direction of motion for each of the two carts following the collision. You
should also predict whether the speed of each cart will increase or decrease. Discuss with
your group whether your answers make sense. Write a sentence or two summarizing your
group discussion on each case.
Please read the following scenarios carefully….
The mass of cart #1 is equal to the mass of cart #2. These two carts are moving as
follows before the collision: cart #1 is moving to the right at 5 m/s, cart #2 is stationary.
The carts do not stick together after the collision.
1.
2. The mass of cart #1 is half of the mass of cart #2. These two carts are moving as
follows: cart #1 is moving to the right at 7 m/s, cart #2 is stationary. The carts do not
stick together after the collision.
3. The mass of cart #1 is half of the mass of cart #2. These two carts are moving as
follows: cart #2 is moving to the right at 9 m/s, cart #1 is moving to the left at 9 m/s .
The carts do not stick together after the collision.
4. The mass of cart #1 is equal to the mass of cart #2. These two carts are moving as
follows: cart #1 is moving to the right at 6 m/s, cart #2 is moving to the left at 6 m/s.
The carts do not stick together after the collision.
5. The mass of cart #1 is equal to the mass of cart #2. These two carts are moving as
follows: cart #1 is moving to the right at 6 m/s, cart #2 is moving to the left at 6 m/s. The
carts stick together following the collision.
Part II - Conservation of Momentum during an Explosion.
WHEN OPENING THE FOLLOWING MOVIE, CHOOSE TO LOCATE 2
OBJECTS, SINCE WE WILL BE TRACKING TWO DIFFERENT CARTS.
For this activity you will need a movie called "explosion.mov" . You can get it off of the
CD (go to VideoPoint folder, then Movies, then look for it in the list). You can also
transfer it from the course webpage (Go to “class activities”, scroll down to the bottom of
the page, RIGHT CLICK on the movie, choose “save link as” and watch were the file get
saved to. Once you have the movie file, open the Videopoint software, chose open movie
and open "explosion.mov" .
 1999, K. Cummings
6. The first thing that must be done is to calibrate our measurement tool. There is a
meter stick shown below the tracks. Use this as your known length. Click on the ruler
icon and follow the instructions that appear on the computer screen. Do not change “scale
origin” or “scale type”.
7. Advance the movie a few frames, until you can see that the two carts have clearly
separated from one another. Now collect some position data for each cart. This is done
by first clicking on one cart, then the other cart, then the movie frame will advance. You
need to always click on the carts in the same order. Take your data carefully to get a good
result the first time around. To do this, center the cursor over a point on the cart on the
right. Click on the point you have chosen. Now do the same for the cart on the left.
Once you have clicked on the second cart, the movie will advance to the next frame.
Collect about 8 data points for each cart.
8. Generate and sketch plots of the x-velocity of both carts.
9. Does either cart have a non-zero velocity in the y direction? How do you know?
10. Estimate the average velocity in the x direction for each of the two carts from your
graphs.
11. Calculate the final momentum of the cart on the right (m= 510.2 grams). Calculate
the final momentum of the cart on the left (m = 1020.2 grams). What is the total final
momentum of the two cart system? Show all of your work in doing these calculations.
12. What was the total momentum of the system before the explosion? Is momentum
conserved in this case? In light of the fact that there was an explosion in this system,
does your answer make sense? Justify your answer using complete sentences.
13.
What was the momentum of the cart on the right before the explosion? What was
the momentum of the cart on the right after the explosion? If you chose only the cart on
the right as your system, would momentum have been conserved in the explosion?
Explain why your answer makes sense in terms of internal and external forces.
14.
What was the momentum of the cart on the left before the explosion? What was
the momentum of the cart on the left after the explosion? If you chose only the cart on
the left as your system, would momentum have been conserved in the explosion?
Explain why your answer makes sense in terms of internal and external forces .
 1999, K. Cummings