What is the most common form of waste energy$?$

Calculate the efficiency of the energy. efficient lamp from the data shown in 

A coal-fired power station produces $100\mathrm{MJ}$ of electrical energy when it is supplied with $400\mathrm{MJ}$ of energy from its fuel. Calculate its its efficiency.

A lamp of $10\%$ efficient, how much electrical energy must be supplied to the lamp each second if it produces $20\mathrm{J}$ of light energy per second$?$

The object's g.p.e. increasing, decreasing or remaining constant$?$ An apple falls from a tree. With example.

The object's g.p.e. increasing, decreasing or remaining constant$?$ An aircraft flies horizontally at a height of $9000 \mathrm{m}$. with example.

The object's g.p.e. increasing, decreasing or remaining constant$?$ A sky-rocket is fired into the sky. With example.