Physics Question from IGCSE

Tell us what you think and we can then see if you are right or not.
You will need to mention Archimedes' Principle in there somewhere.

Reply 2

OP

Original post by Stonebridge

Tell us what you think and we can then see if you are right or not.
You will need to mention Archimedes' Principle in there somewhere.

So far I have put this:
The ship’s weight has increased so the gravitational field strength acting upon it is stronger.

If this is correct however, it would still only be one mark.

Reply 3

Not the 'field strength', just the actual gravitation force, in other words, its weight mg. It's greater with all the cargo. It's m that has increased, not g. (g is the field strength)
So how does Archimedes get into this? Why does the ship not sink to the bottom?

Reply 4

OP

Original post by Stonebridge

Not the 'field strength', just the actual gravitation force, in other words, its weight mg. It's greater with all the cargo. It's m that has increased, not g. (g is the field strength)
So how does Archimedes get into this? Why does the ship not sink to the bottom?

I don't think we have learnt about Archimedes Principle, but the question beforehand was still about the boat and it was taking aboutupthrust and pressure difference = height x density x g so I think the answer may be about pressure difference but I'm not sure.

Perhaps maybe I need to bring in the equation pressure = force / area. There will be increased pressure because the area stays the same but the force increases, causing pressure to push the boat down?

(edited 4 years ago)

Reply 5

The question is seemingly about Archimedes' Principle, but there is a connection to pressure at a depth, which is equal to hdg, as you say.
With a question like this which asks you to 'explain', there is a little context needed that tells how we are expected to explain, and in what terms.
As it is GCSE, I have assumed it would be part of a study of Archimedes.
In terms of pressure at a depth, then the deeper you go in the water, the higher the pressure. P=hdg and it is h, the depth, that is increasing.

So what determines the amount of upthrust? The boat needs this to stop sinking.

Reply 6

OP

The upthrust must be equal to the weight of the boat otherwise unbalanced forces would cause it to sink

Reply 7

Yes. So firstly, the heavier the boat the more upthrust is needed.

Secondly, the deeper you go, the greater the pressure. P=hdg

And finally, as you have suggested, Pressure = force / area
which means that if pressure increases, so does the available force to support the boat. (The area is the effective area of the bottom of the boat, which can also change as the boat goes deeper, and would also tend to increase the force)
So from all this, can you see how it is possible to explain why the boat sinks lower?

Reply 8

OP