Friction, Total Energy and Potential Energy

If the pair of track magnets is located at distance x = 40 cm, for example, the diagrams should look similar to these ones:

Now try to imagine the total energy with very low friction. Draw a line that represents the total energy of the car if no friction were present. You should get something like the graph below:

As seen from the diagram, away from the magnets (at x < 20 cm and x > 60 cm) where the potential energy is zero, the kinetic energy equals the total energy of the car.

Now make a sketch of the potential energy diagram of the car by subtracting the kinetic energy from the total energy (applying the conservation law). You should get something like the graph below:

Answer the following questions:

• How is this potential energy diagram different from the ones for the attractive situation?
• Explain the reason for this difference in terms of how the energy of the car changes.