a]
[tex]E=\frac{1}{2}mv^2 \ \ |\cdot2\\\\mv^2=2E \ \ |:v^2\\\\m=\frac{2E}{v^2}[/tex]
b]
[tex]E=\frac{1}{2}mv^2 \ \ |\cdot2\\\\mv^2=2E \ \ |:m\\\\v^2=\frac{2E}{m}\\\\v=\sqrt{\frac{2E}{m}}[/tex]
