# For a submarine to stay submerged, it must be neutrally buoyant,?

which means it is maintaining a careful balance between its weight and the buoyant force of water pushing it toward the surface. If a submarine has an enclosed volume of 881.966 m3, how much must it weigh to stay submerged? (Use 1000 kg/m3 for the density of water.)

Please help, I've tried so many formulas and I can't get it right

### 8 Answers

- TomLv 74 months ago
NO---It has to be heavier than the weight of the water it displaces-----like a rock---which also stays submerged. The Neutrally buoyant thing is a safety factor------so the HEAVIEST it can be is still not enough to keep it sunk to where the sub CANT get back up. There usually is a built in, small POSITIVE buoyancy. The dive planes and control surfaces maintain a downwards force as the sub moves forward. SO it there is engine trouble the sub will eventually surface. and not get stuck on the bottom. A Neutral Buoyant sub has the ability to "Hover" at any depth. ------Simple forward motion and control planes allow it to adjust depth without messing with the ballast tanks---pumping water in or out.

- electron1Lv 74 months ago
Buoyant force = 1000 * 881.966 = 881,966 N

Weight = mass * 9.8

mass * 9.8 = 881,966

Mass = 881,966 ÷ 9.8

The mass of the submarine is approximately 90,000 kilograms.

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- MorningfoxLv 74 months ago
If you think about formulas out of a book, you aren't going to understand and learn the situation. You need to use logic, so that you can create the formula from your brain.

- billrussell42Lv 74 months ago
the weight must equal the weight of the displaced water, which is just:

W = 881.966 m³ x 1000 kg/m³ = 881966 kg (this is actually the mass)

(the 6 digit precision is silly, the density number is accurate to 3 places, so the answer should 882000 kg)

If you want the weight in Newtons, multiply by 9.8 to get

882000 kg x 9.8 N/kg = 8640000 N

- HenryLv 54 months ago
That's probably the wrong formula. The large submarines are all hoaxes, only the toy ones really work.

- flyingtiggerukLv 74 months ago
To be neutrally buoyant it has to have the same mass as the displaced volume of water which is volume * 1000.

I agree with Bill on the accuracy but it would mean that the answer could have been shown as 8.6 * 10 ^ 6 N which has ALMOST the same precision as gravity at 9.8 N/kg In the current form the accuracy is ambiguous.