Question 3
In case (d) of activity 15.3 the spring balance reading fell when the object was immersed in water. In the light of case (c), what does this establish?
The right answer is the one marked above.
That an upward force acts on the object. In case (c) we saw the reading fall when an upward force was applied — so in (d) an upward force must be acting too.
The mass has not changed at all — it is the same object. And a downward force would have made the reading rise, not fall.