Question

If a cart has 100 Joules of mechanical energy and 60 Joules of that is potential energy, how much kinetic energy must it have?

Answer 1

The mechanical energy is defined as the sum of the potential energy and the kinetic energy, then we have:

$E_{\text{mec}}=K+U$

where K is the kinetic energy and U is the potential energy.

Plugging the values given for the mechanical and potential energy and solving for the kinetic energy we have that:

$\begin{gathered} 100=K+60 \\ K=100-60 \\ K=40 \end{gathered}$

Therefore 40 J are kinetic energy.