Investigation 11C: Elastic collisions

Essential questionsHow can we predict the outcome of an elastic collision?
In an inelastic collision kinetic energy is lost, but momentum is conserved. Is the same true for perfectly elastic collisions? In this investigation, explore how the total kinetic energy and momentum of a closed system is affected by a perfectly elastic collision.
Part 1: Simulation of elastic collisions between balls

Part 1: Simulation of elastic collisions between balls
  1. Run the simulation using mgreen = 5 kg, 10 kg, and 50 kg with mred = 5 kg, and mgreen = 5 kg with mred = 10 kg and 50 kg.
  2. For each combination, record in a table the masses and initial and final values for velocities, ptotal and Ek total.
  3. Examine the table for patterns in the data.
  1. Describe the velocities before and after the collision when: the masses are equal; the green ball has less mass; the green ball has more mass.
  2. If this had been an inelastic collision investigation, how would your energy values differ?
  3. As a result of the collision, does the total momentum of the system increase, decrease, or remain the same? Does the total kinetic energy increase, decrease, or remain the same?
In this interactive simulation a green rubber ball has collides with the stationary red rubber ball in a model of a perfectly elastic collision. Both balls may move after the collision. Investigate what happens as a result of an elastic collision when the balls have the same or different masses.
Part 2: Elastic collisions between carts

A collision between two carts is nearly elastic, but not completely. How well can a physical situation approximate a perfectly elastic collision? Explore how the total kinetic energy and momentum of this closed system is affected by an elastic collision between the carts.
  1. Attach a magnetic bumper to the front of each smart cart, then set a red cart and a blue cart on a level track with the magnetic bumpers facing each other, as shown. Adjust the track feet to make sure the track is as level as possible.
image
  1. Open the experiment file 11C_ElasticCollisions, and then power-on the Smart Carts and connect your Smart Carts to your computer using Bluetooth.
  2. Begin collecting data, gently pushing the red cart toward the blue cart and allowing them to collide. Stop recording data once carts have collided.
  3. Run the experiment for different combinations of masses for the two carts. Use a data table to record the velocity for each combination.
  4. Examine the table for patterns in the data as in Part 1.

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