# Rocket Sled Lab

 Materials: Computer and School Network Time Allotment: 3 Class Days

### Purpose:

The purpose of this lab is to investigate the conservation of momentum principle for the impulse experienced by a rocket and sled.

This lab must be done on a Macintosh computer connected to the school network or upon a computer in the Science Computer Lab. To prepare for the lab, do the following steps.

• Log onto the school network in the usual manner.
• Open the Interactive Physics application.
• Choose Open... from the File menu. Navigate to the Hewitt Simulations folder and open the file titled Rocket-Sled I by double-clicking on its name.

### Situation A:

A mining company uses rocket-powered sleds to transport mineral ore to a processing plant on an ice-covered planet. Two kinds of sleds are used, an engine-sled with a driver and an unmanned freight-sled. Both sleds are equipped with heavy-duty bumpers that have adjustable elasticity. To transport the ore, the driver drives the engine-sled into a head-on collision with the freight-sled. The collision propels the freight-sled across the icy planet surface.

### Make a Prediction:

1. The engine-sled and freight have the same mass. The engine-sled, traveling at 4.00 m/s , collides with the freight-sled. The collision brings the engine-sled to a complete stop. Predict the speed of the freight-sled after the collision. Place a check next to your prediction.

1. 0.00 m/s
2. 2.00 m/s
3. 4.00 m/s
4. 8.00 m/s

 Run Simulation: Set Initial dpeed of engine-sled to 4.00 m/s. Set the Mass of engine-sled to 2.00 x 103 kg. Set Collision to Elastic. Click the Run button and observe the simulation.

2.Was your prediction correct? Explain the result in terms of the conservation of momentum.

3. How will doubling the speed of the engine-sled affect the result? The engine-sled and the freight-sled still have the same mass, except mow the engine-sled is traveling at 8.00 m/s. The collision brings the engine-sled to a complete stop. Predict the speed of the freight-sled after the collision. Place a check next to your prediction.

1. 0.00 m/s
2. 4.00 m/s
3. 8.00 m/s
4. 16.00 m/s

 Run Simulation: Click the Reset button. Set Initial speed of engine-sled to 8.00 m/s. Set Mass of engine-sled to 2.00 x 103 kg. Set Collision to Elastic. Click the Run button and observe the simulation.

4. Was your prediction correct? In terms of conservation of momentum, explain how doubling the speed of the engine-sled affected the result.

5. Calculate the momentum of the emgine-sled and freight-sled before and after the collision. Use the Step forward and Step backward buttons to obtain the necessary data from the simulation to do the calculations. Show your work below in an organized fashion.

6. Describe the distinction between an elastic and an inelastic collision in your own words.

###### Table 1 Elastic Collision

 Mass* (kg) Speed (m/s) Momentum (kg*m/s) Mass (kg) Speed (m/s) Momentum (kg*m/s) Momentum* (kg*m/s) Before Colision 2.00 6.00 12.00 2.00 0.00 0.00 12.00 After Colision ______ ______ ______ ______ ______ ______ ______

*All mass and momentum values are multiplied by 104.

Mass*

(kg)

Speed

(m/s)

(kg*m/s)

Mass

(kg)

Speed

(m/s)

(kg*m/s)

(kg*m/s)

Before

Collision

______

______

______

______

0.00

0.00

______

After

Collision

4.00

4.00

16.00

2.00

4.00

8.00

24.00

### Situation B:

• To get ready for Situation B (and Situation C), open the lab file titled Rocket Sled II; use the Open... command found in the File menu.

To send ore on its way to a newly built processing plant, the engine-sled driver must propel the freight-sled across a deep crevasse. The driver's goal is to propel the freight-sled across the crevasse while keeping the engine-sled safely away from the edge of the crevasse. The engine-sled driver must carfully control the collision--a miscalculation could result in the loss of the freight-sled or even of the engine sled itself!

### Make a Prediction

7. Using your knowledge of collisions and the law of conservation of momentum, predict what the engine-sled driver should do to safely propel the freight-sled across the crevasse while ensuring the engine sled itself is not lost. Assume no external forces (such as friction) act on the rocket-sleds during the collision. Assume the rocket-sleds slide across the ice without friction. What is your prediction?

1. The driver should ensure the collision is elastic.
2. The driver should ensure the collision is inelastic.
3. The driver should ensure the collision is elastic and the masses of the two rocket-sleds are equal.
4. The driver should ensure the collision is elastic and that the mass of the engine-sled is greater than the mass of the freight-sled.

 Run Simulation: Set values for Mass of engine-sled, Initial speed of engine sled, and Collision according to your prediction above. Click the Run button and observe the simulation. At this point, do not worry if the freight-sled does not make it across the crevasse, only concern yourself with making sure the engine-sled is not lost. Repeat the simulation until you find a way to ensure the engine-sled is not lost. Remember to click the Reset button before making any changes to the simulation.

8. Was your original prediction correct? Explain what conditions will ensure the engine-sled is not lost.

9. Explain what conditions will result in all of the engine-sled's momentum being transferred to the freight-sled.

## Situation C

At the end of the day, the engine-sled driver also wishes to cross the crevasse in order to go home. The driver wishes to propel both the freight-sled and the engine-sled accross the crevasse.

 Run Simulation: Experiment with various settings for Mass of engine-sled, Initial speed of engine-sled, and Collision until you find the conditions that result in both the engine-sled and the freight-sled making across the crevasse. Remember to click the Reset button before making any changes to the simulation.

10. Completely describe the conditions that will result in both the engine-sled and the the freight-sled making it across the crevasse.

### Conclusion:

Discuss the conservation of momentum and its application to collisions. Do more than state the law. Illustrate the law by using numerical values of mass and velocity (both before and after the collision) to show what is meant by momentum conservation. Do an illustration for both an elastic and an inelastic collision.