The correct equation for terminal velocity (\( V_t \)) of an object falling under the influence of gravity in a viscous medium is generally given by:
\[ V_t = \sqrt{\frac{2mg}{\rho C_d A}} \]
where:
- \( m \) is the mass of the object,
- \( g \) is the acceleration due to gravity,
- \( \rho \) is the density of the fluid,
- \( C_d \) is the drag coefficient,
- \( A \) is the cross-sectional area of the object.
From the provided options, the equation that resembles the correct form for terminal velocity is:
\[ V_t = \sqrt{\frac{w}{2dAC_d}} \]
where \( w \) can be interpreted as the weight (which is \( mg \)), \( d \) as the density of the fluid, \( A \) as the cross-sectional area, and \( C_d \) as the drag coefficient.
Thus, the correct response is:
\[ V_t = \sqrt{\frac{w}{2dAC_d}} \]