# If an object with a mass of  3kg  changes speed from 4m/s to  9m/s, by how much does its kinetic energy change?

Feb 20, 2017

Because kinetic energy is given by $\frac{1}{2} m {v}^{2}$ regardless of the particular situation involved, the change in kinetic energy here will be
$\Delta K = \frac{1}{2} m {v}_{f}^{2} - \frac{1}{2} m {v}_{i}^{2} = \frac{1}{2} \left(3\right) {\left(9\right)}^{2} - \frac{1}{2} \left(3\right) {\left(4\right)}^{2}$
$\Delta K = 121.5 J - 24 J = 97.5 J$