ANS:D - 4

The ratio of the frictional factor and the coefficient of friction used in the general equation for head loss in a pipe is typically 4. The Darcy-Weisbach equation, which is commonly used to calculate head loss due to friction in a pipe, is expressed as: hf​=f L/D ​V^2/2g​ Where:

• hf​ is the head loss due to friction,
• f is the friction factor,
• L is the length of the pipe,
• D is the diameter of the pipe,
• V is the velocity of flow, and
• g is the acceleration due to gravity.

In this equation, f is dimensionless and represents the frictional factor, while the coefficient of friction is related to the surface roughness of the pipe and other factors affecting friction. The specific value of the frictional factor depends on the flow regime (laminar or turbulent) and the roughness of the pipe wall. In many practical cases, the ratio of the frictional factor to the coefficient of friction is approximately 4.