During a heating period, a gas boiler transfers energy from fuel to radiator water and to a room. The fuel, the water and the room are taken together as a closed system. Assume that every energy store not shown in the table retains its initial energy.
| Energy store | Initial energy | Final energy |
|---|---|---|
| Chemical energy store of the fuel gas | XXX | 95 MJ95\ \mathrm{MJ}95 MJ |
| Thermal energy store of the radiator water | 120 MJ120\ \mathrm{MJ}120 MJ | 145 MJ145\ \mathrm{MJ}145 MJ |
| Thermal energy store of the room | 210 MJ210\ \mathrm{MJ}210 MJ | 225 MJ225\ \mathrm{MJ}225 MJ |
Which value is XXX, the initial energy in the chemical energy store of the fuel gas?
110 MJ110\ \mathrm{MJ}110 MJ
135 MJ135\ \mathrm{MJ}135 MJ
55 MJ55\ \mathrm{MJ}55 MJ
120 MJ120\ \mathrm{MJ}120 MJ
115 exam-style questions on Edexcel GCSE Physics 8.1 Energy transfers and work, covering 8.1.1 Energy stores and transfer diagrams, 8.1.2 Ways of changing a system's energy, and 8.1.3 Work done by forces. Each one has a worked solution and a mark scheme showing where the marks go.