Two trolleys each carry a magnet. The magnets are held close together on a track inside an insulated enclosure. When the trolleys are released, the magnetic force moves them apart.
During the motion, all energy transfers take place within the enclosure.
The table shows the changes in energy stores while the trolleys are moving.
| Energy store | Change in energy |
|---|---|
| magnetic energy store of the magnets | -3.5 J |
| kinetic energy stores of the trolleys | +2.0 J |
| thermal energy stores of the trolleys | +0.4 J |
| thermal energy stores of the track and air | +1.1 J |
Use the data to explain how changing the system boundary from the whole enclosure to only the trolleys and magnets affects the total change in energy. Include the energy transfer pathway from the magnetic energy store in your answer.