Answer
a. $\lambda=\frac{h}{p}=\frac{h}{\sqrt{2m(K)}}$
b. $4.34\times10^{-11}m$.
Work Step by Step
For a nonrelativistic particle, $p=mv$ and $K=\frac{1}{2}mv^2$ so $p=\sqrt{2m(K)}$.
$\lambda=\frac{h}{p}=\frac{h}{\sqrt{2m(K)}}$
b. $\lambda=\frac{6.626\times10^{-34}J \cdot s}{\sqrt{2(9.11\times10^{-31}kg)(800eV)(1.60\times10^{-19}J/eV)}}$
$\lambda= 4.34\times10^{-11}m$
