Answers to AQA GCSE Conservation of energy

2. A saucepan of soup is being heated on a cooker hob. The internal energy store of the metal saucepan gains 2000J of energy, whist the liquid soup increases its energy store by 1500J whilst being heated. Calculate the size of the thermal energy store of the heating element in the hob.

In this case, the total energy outputs are 2000J + 1500J, so 3500J. Therefore, as total energy input = total energy output, the total energy input is also 3500J.

3. A runner has Y amount of energy stored in his muscles as chemical energy. The runner goes for a run, 80% of the chemical energy is mechanically transferred into kinetic energy, whilst 20% of the energy is transferred to the thermal energy store of the surroundings by radiation. The thermal energy store of the surroundings increases by 500J during the run. 

a) Calculate the gain in the kinetic energy store

Thermal energy store = 20%, so this is 500J. 

Therefore 80% is four times greater, so it will be 2000J. 

b) Calculate the size of Y (chemical potential energy store.)

2000J + 500J = 2500J.

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