The displacement of a wave is given by y = 0.004 (200t - 2x) , in...

The standard equation of a wave traveling in the positive x-direction is $y = A \sin(\omega t - kx)$.

The given equation is $y = 0.004 \sin(200t - 2x)$.

Comparing the given equation with the standard equation, we get:
$\omega = 200$ rad/s
$k = 2$ rad/m

The negative sign between the $t$ and $x$ terms indicates that the wave is traveling in the positive x-direction.

The velocity of the wave is given by $v = \dfrac{\omega}{k}$.

$v = \dfrac{200}{2} = 100$ m/s.

Therefore, the wave is traveling with a velocity of $100$ m/s in the positive x-direction.