$$ \put \begin{cases} \KE : \text{Kinetic Energy}\\\end{cases} $$$$ \begin{cases} m&=150\ut{g}\\v_i&=5.2\ut{m/s}\\\KE_f&=\frac{1}{2}\KE_i\end{cases} $$$$\ab{a}$$$$ \begin{aligned}\KE_f&=\frac{1}{2}\KE_i\\\frac{1}{2}m{v_f}^2&=\frac{1}{2}\cdot\frac{1}{2}m{v_i}^2\\\end{aligned} $$$$ \begin{aligned}v_f&=\sqrt\frac{1}{2}\cdot{v_i}\\&=\frac{v_i}{\sqrt2}\\&=\frac{13\sqrt2}{5}\ut{m/s}\..