Question

The viscous drag is:

• A. inversely proportional to the velocity gradient.
• B. directly proportional to the surface area of layers in contact.
• C. independent of nature of liquid.
• D. perpendicular to the direction of liquid flow.

Answer 1

Answer: (B)

directly proportional to the surface area of layers in contact.

The viscous drag force can be written as below:
$F=\eta A\left(\frac{dV}{dX}\right)$ where, F is viscous drag force (or tangential force)
$\eta$ is coefficient of viscosity
$A$ is surface area of layers in contact
$\frac{dV}{dX}$ is velocity gradient
$\eta$ is property of liquid.
So, we can see that drag is directly proportional to the velocity gradient, surface area and nature of liquid. Drag force acts in opposite direction of liquid flow.