4 How do you get the weight of the heavy solid when it is completely immersed in the liquid?

Answer 1

Depends on the circumstances.

I like to calculate things because it's easy and quick...and I hate lab work. So given the choice, I'd find what the solid is made of...find it's density (30seconds work with a decent physical chemists' almanac or wikipedia) then measure the solid's dimensions. Calculate the solid's volume and then finally it's mass using the aforementioned density.

Which sounds harder than it is. You could do it in minutes.

But things are not always so easy...maybe you don't know what the solid is, or if it is impure...or maybe it's an odd shape not easily measured or at a temperature that you don't control. Occasionally you'll just get a really weird compound that has no recorded density. Rare but happens.

This way you'll get the mass of the object...which at ground-level is almost identical to the weight of the object. Now...you can measure the weight using a spring balance or whatever you please whilst submerged and it'll be correct....but in that case the weight will be nowhere near the mass. So it depends what is sincerely meant when you say "weight".

This is because (crudely put) weight describes how much force you must apply to support an object. That force is less when the object is submerged and so it weighs less. Mass, however, is constant for the object.

I apologise if that's a patronising distinction but it was required a mention. When I see "weight" used in a question like this, I assume mass is meant. But perhaps it's just a sneaky question.