Answer
$\mathbf{u}\cdot\mathbf{v}=20$
Work Step by Step
$\mathbf{u}\cdot\mathbf{v}=\|\mathbf{u}\|\|\mathbf{v}\|\cos{\theta}$
$\|\mathbf{u}\|=8$
$\|\mathbf{v}\|=5$
$\cos{\theta}=\cos{\frac{\pi}{3}}=\frac{1}{2}$
therefore,
$\mathbf{u}\cdot\mathbf{v}=8\times5\times\frac{1}{2}=20$
