Question

solving dimensionless analysis problem, how to decide whether to use M-L-T or F-L-T?

Answer 1

The fundamental dimensions are

M - mass (kg)

L - Length (m)

T - Time (s)

F - force (N)

Mass and weight are convertible into each other

Force = mass x g

1N = kg-m/s2

F = MLT^-2

Or

M = FL^-1T²

You can use only one system at a time either MLT or FLT

Force is derived in MLT system.

Mass is derived in FLT system

If F is chosen as a primary dimension then use FLT system

If M is chosen as a primary dimension then use MLT system

Use MLT system

If mass is in SI and American units are kg and lbm respectively

Use FLT system

If Force is in SI and American units are N and lbf respectively.