Question

A stone weighing $1kg$is dropped from rest from a height of $4m$ above the ground. When it has free-fallen $1m$, what will be its total energy with respect to the ground?

Answer 1

1. Energy is conserved in free-fall.
2. Thus total energy will be the same at all stages of falling.
3. Total energy is the sum of potential energy and kinetic energy.
4. At the initial point, the stone has only potential energy, as it is at rest.

Calculation of potential energy at the initial point:

Potential energy, PE $$\begin{gathered} =mgh \\ =1\times 10\times 4J \\ =40J \end{gathered}$$

So, Total energy after free-fall of $1m$will be $40J$.