You don’t use the possessive with scientific units. In fact, you probably don’t have to use the possessive with any units, although there are figures of speech that appear to do so, e.g. a day’s pay for a day’s work.
In any event, the abbreviations for SI units always appear in their simple form directly after the number they apply to. Plural and possessive forms are not used.
BTW, it’s 10kg of mass, not weight. In ordinary life we use the term weight more freely, so it’s perfectly okay to say that a person “weighs 70kg”. Even in
science and engineering journals, you can sometimes see expressions like this in the description of everyday objects.
However, if you are writing for a technical audience, you should follow the appropriate SI style.