A friction brake brings a spinning exercise-bike flywheel to rest. The flywheel, brake and surrounding air are treated as a closed system. All of the energy initially in the kinetic energy store of the flywheel is transferred to the three thermal energy stores shown.
| Thermal energy store that increases | Increase in energy |
|---|---|
| brake pad | 420 J |
| flywheel | 300 J |
| surrounding air | 180 J |
What fraction of the initial energy in the kinetic energy store of the flywheel is transferred to the thermal energy store of the flywheel?
0.330.330.33
0.470.470.47
0.710.710.71
0.200.200.20