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Physics 111 ON 1

November 9, 2020

Lab #4 Momentum, Energy & Collisions

Objectives:

· Observe collisions between two carts, testing for the conservation of momentum.

· Measure energy changes during different types of collisions.

· Classify collisions as elastic, inelastic, or completely inelastic.

Preliminary Questions:

1.) Consider a head-on collision between two identical billiard balls. Ball 1 is initially in motion toward ball 2, which is initially at rest. After the collision, ball 2 departs with the same velocity that ball 1 originally had. Disregard any friction between the balls and the surface. What happens to ball 1? What happens to ball 2?

Ans:

2.) Sketch a position vs. time graph for each ball in Preliminary Question 1, starting with the time before the collision starts and ending a short time after the collision.

ANS:

3.) Based on your graph from Preliminary Question 2, is momentum conserved in this collision? Is kinetic energy conserved?

Method: After measuring the masses of the Dynamic Carts and recording the values in Table 1, the carts were labeled Cart 1 and Cart 2. The Dynamics Track was set up, and using a level, adjusted to be horizontal. A motion detector, with the sensitivity set to Track, was placed at each end of the track, and connected to the digital ports of the Vernier interface. The file “18 Momentum Energy Coll” was opened in the Logger Pro software. The motion detectors are “zeroed” so that the same coordinate system is being measured with both motion sensors.

In each of the three parts, the two carts were set up so that Cart 2 would be placed in the middle of the track, and Cart 1 would be given a gentle push so that it would bump into Cart 1.

· In Part I, both carts have opposing magnets facing each other. The carts repel each other before they collide.

· In Part II, the two carts have “hook-and-pile”, or Velcro bumpers facing each other, so that they stick together after colliding.

· In Part III, one cart has magnet bumpers, and the other car has velcro bumpers, so that they do not repel each other, nor stick together.

For each section, data was selected from the velocity graphs, and the average velocity before and after the collision was recorded in the Table

Data Tables and Graphs:

Figure 1 a Magnet Bumpers Position & Velocity Plots Trial 1

Figure 1 b Magnet Bumpers Position & Velocity Plots Trial 2

Figure 2a Hook & Pile Bumpers Position & Velocity Plots – Trial 3

Figure 2a Hook & Pile Bumpers Position & Velocity Plots – Trial 4

Figure 3a Combined Hook/Pile & Magnet Velocity and Position Plots – Trial 5

Figure 3b Combined Hook/Pile & Magnet Velocity and Position Plots – Trial 6

Table 1

Mass of Cart 1 0.575 kg

Mass of Cart 2 0.579 kg

TABLE 2

TABLE 3

Data Analysis:

1) For each run, determine the momentum (mv) of each cart before the collision, after the collision, and the total momentum before and after the collision. Calculate the ration of the total momentum after the collision to the total momentum before the collision. Enter the information in Table 2. (Use the appropriate mass for each cart listed in Table 1, and the appropriate average velocities listed in Table 2.)

2) For each run, determine the kinetic energy (KE = ½ m v2 ) for each cart before and after the collision, and record the data in Table 3. Calculate the ratio of the total kinetic energy after the collision to the total kinetic energy before the collision. Record the data in Table 3.

3) If the total momentum for a system is the same before and after the collision, we say that momentum is conserved. If the 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 the kinetic energy were conserved, what would be the ratio of the total kinetic energy after the collision to the total kinetic energy before the collision?

5) Inspect the momentum ratios in Table 2. 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 ration should be close to one, however. Is momentum conserved in your collisions?

6) Repeat the questions from 5) for the case of kinetic energy, using the kinetic energy ratios in Table 3. Is kinetic energy conserved in the magnetic bumper collisions? How about the hook-and-pile collisions? Is kinetic energy consumed in the third type of collision studies? Classify the three collision types as elastic, inelastic, or completely inelastic.

Conclusions: