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In an exam on seismics and earthquake proof design I had a couple of days ago, there was a question on multiple mass oscillators in the form of a simply supported beam of length $L$, stiffness $EI$ and two point masses $M$ at the points $x_1=\frac{1}{3}L$ and $x_2=\frac{2}{3}L$.

sketch of the beam and masses

Although I know, how to solve such a system, I was a bit confused about the unit of measurement of the mass. Both "masses" featured a value of $M=1'000$ $kg\cdot s^2/m$. At first I thought it was a typo meant to be $[kg\cdot m/s^2]$, which I would have interpreted as $M$ representing a force, i.e. $M=m\cdot g$.

However this denotation appeared over and over again on this exam (and of recent years as well).

A classmate assumed, you had to multiply this "mass" $M$ with the readings from an accelerometer. This would make sense to me in regards to the units but not as a logical principle.

Why would you denote the mass-property of an object neither by its mass, nor by its weight? Is anyone around here familiar with such a concept either in seismics or any other field?

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