Justify in one sentence that hydropower (hydro electricity) is a renewable source of energy.

List any four sources of energy which are selected for use for a given activity. 

1. Energy to run a cycle
2. Energy to run a car
3. Energy to cook food 
4. Energy to work on 

Classify the following as renewable and non-renewable sources of energy.
Coal, flowing water, geothermal energy, nuclear energy, biogas, natural gas, petroleum, ocean waves, wood, flowing wind, cooking gas, biomass, hydroelectric power.

'Replenishment of energy source like wood takes a long time but it is considered as renewable source of energy.'  Comment.

What constitutes a source of energy?

State the two forms in which energy is mainly utilised at our homes.

When a body falls freely to the ground, its velocity reduces to zero and the sum total of kinetic energy and potential energy also becomes zero. Does it violate the law of conservation of energy?

Justify in one sentence that hydropower (hydro electricity) is a renewable source of energy.