If you are told that a boat can displace 75 mL of water, how many pennies can it hold before sinking?

Question

dape · Answer

Archimedes:
"Any object, wholly or partially immersed in a fluid, is buoyed up by a force equal to the weight of the fluid displaced by the object."
The weight of 75 ml of water is about the weight corresponding to 75 grams. If we say a penny weighs 1 gram it can hold 75 pennies.

anonymous · Answer

What is the density in the equation?

dape · Answer

I just guessed that a penny has a mass of 1 gram. And 1 ml of water is almost exactly 1 gram. I think it's like 0.998 grams, but who cares.

anonymous · Answer

don't u need that info to solve this question?

dape · Answer

I solved it roughly. If you want you can look up the mass of the penny in grams and use that to find a more precise answer.

anonymous · Answer

oh ok

anonymous · Answer

what is the volume in the problem?

anonymous · Answer

@dape

dape · Answer

You don't need the volume, since 1 ml of water ≈ 1 g of water :)

anonymous · Answer

so is the answer 30 pennies?

dape · Answer

Yes, the mass of a penny is apparently 2.5 g, so the answer should be 30 pennies, not 75 as I said in my rough estimate.

anonymous · Answer

Thank you!

anonymous · Answer

can i ask you one more @dape?

dape · Answer

Sure, is it the question you posted about mercury?

anonymous · Answer

Yes!