Worksheet #4 – Different Prediction Models

Goal: To investigate the possibility of using the Work-Kinetic Energy, Impulse-Momentum and the Conservation of Energy theories to predict the altitude of a launched rocket using the same given information as we used with kinematics (“Big Four”). These questions are a guide in helping you develop a model and your thoughts should not be limited to just answering them. Discuss whether the model can be used or not be used to predict, if you need more information, must use kinematics at some point in the process, etc…

Stage 1 – Impulse-Momentum

1. What is the impulse rating of the C6-5 engine we used?

2. List the impulse-momentum equation. Can you calculate the impulse of the rocket engine? How?

3. What forces are involved in changing the momentum of the rocket during launch?

4. Do you need to know the net force on the rocket to calculate the impulse or just the force of the engine?

5. How can you find the velocity of the rocket using this model?

6. Can you still use the kinematics equation to find the altitude of the rocket?

7. Discuss how you can use the impulse-momentum model to find the velocity and then the altitude of the rocket.

8. Now you will develop a prediction spreadsheet using the Impulse-Momentum theory. Using your previous spreadsheet, change the Acceleration column to Impulse (N-s).

9. Enter a formula in row 19 of the Impulse column that will calculate the impulse of the rocket for the time interval.

10. Using the Impulse-Momentum theory enter a formula in to calculate the velocity of the rocket in row 19.

11. What is the maximum altitude of the rocket? ____________ When did this occur? ________

12. Compare your results using this model with the kinematics prediction. Discuss.

Stage 2 – Work-Kinetic Energy

1. List the Work-Kinetic energy formula and the formula for work.

2. What forces are doing work during a rocket launch?

3. Are you given enough information to make a prediction using this formula?

4. What if we looked at changing the altitude instead of the time? Would this help?

4. Discuss how you would use the Work-Kinetic Energy theorem to predict altitude.

Stage 3 – Conservation of Energy

**Discuss things in general terms such as PEg is increasing, PEeng + KE + PEg - KEd

1. Name the types of energies during a rocket launch.

2. Does the Conservation of Energy hold true during the rocket launch?

3. What is the initial total energy of the rocket before the launch? What is the potential energy of the engine?

4. What is the total energy of the rocket during engine burn?

5. Explain what happens to the individual energies as the engine burns. Increase, decrease, zero?

6. What is the total energy of the rocket after engine burnout and before apogee?

7. Explain what happens to the energies as the engine climbs toward apogee. Increase, decrease, zero.

8. What is the total energy of the rocket at apogee?

9. How might you calculate the energy loss due to drag?

10. Discuss how you might use the Conservation of Energy to calculate the altitude of the rocket.