We will have the following:
a)
[tex]\begin{gathered} k=\frac{1}{2}mv^2\Rightarrow k=\frac{1}{2}(68.1kg)(3.90m/s)^2 \\ \\ \Rightarrow k=517.9005J\Rightarrow k\approx517.90J \end{gathered}[/tex]So, the energy is approximately 517.90 Joules.
b.
[tex]\begin{gathered} W=\frac{1}{2}(68.1kg)(2\ast3.90m/s)^2-\frac{1}{2}(68.1kg)(3.90m/s)^2\Rightarrow W=2466.3015J \\ \\ \Rightarrow W\approx2466.30J \end{gathered}[/tex]And the work required to double its speed is approximatley 2466.30 Joules.
