What do you call the process of finding the magnitude of fy

Answer - vector resolution

Any vector suppose f if lies at some angle, then

fy = F x cos or sin (theta)

and fx = F x cos or sin (theta)

Process of finding the value of component of any vector quantity is called Vector Resolution.

The process of finding the magnitude of Fy is called vector resolution.

Explanation:

Given a vector with a magnitude equals to F which forms an angle equals to θ with the x-axis, then it can be decomposed into two smaller vectors (Fx and Fy) as follows:

Fx = F*cosθ (placed on the x-axis)

Fy = F*sinθ (placed on the y-axis)

This process is called vector resolution.