Question

A 4.5 newton object is placed in a tank of water. If the water exerts a force of 4.0 Newtons on the object, will the object sink or float? Why?

Answer 1

It will sink. Why? because the buoyant force is not equal to the weight of the object.

Answer 2

This is exactly the same principle as the question I replied to a while back (you just gave me a medal for it...)

In essence if a body is more dense than water it will sink. If it less dense it will float.

If less dense then it will immerse up to the point where the weight of the volume of the water which it displaces is exactly equal to the weight of the body. Thus the buoyancy force and the weight are equal and opposite - so the body remains immersed to that level - i.e. it floats.

If more dense then, as it becomes immersed the buoyancy force will increase as the volume immersed increases. However, at the point where the body is totally immersed, the buoyancy force is still LESS than the weight of the body, and hence the net force is still 'downwards' so it sinks.