Mechanical energy
 Definition 1: Mechanical energy
Mechanical energy is the sum of the gravitational potential energy and the kinetic energy of a system.
Quantity: Mechanical energy (${E}_{M}$) Unit name: Joule Unit symbol: J
Mechanical energy, ${E}_{M}$, is simply the sum of gravitational potential energy (${E}_{P}$) and the kinetic energy (${E}_{K}$). Mechanical energy is defined as:
Tip:
You may see mechanical energy written as U. We will not use this notation in this book, but you should be aware that this notation is sometimes used.
Example 1: Mechanical energy
Question
Calculate the total mechanical energy for a ball of mass 0,15 kg which has a kinetic energy of 20 J and is 2 m above the ground.
Answer
Analyse the question to determine what information is provided

The ball has a mass $m=0,15$ kg

The ball is at a height $h=2$ m

The ball has a kinetic energy ${E}_{K}=20$ J
Analyse the question to determine what is being asked
We need to find the total mechanical energy of the ball