# Weight of the boat in water.

1. Oct 23, 2007

### alister718

if i tell you that water displaced in terms of (Volume initial and Vfinal ) is Vf how would i be able (if you can) to calculate the weight of the boat?

2. Oct 23, 2007

### mgb_phys

If the boat is floating it's weight is equal to the weigth of the volume of water displaced.
If you know the volume and density of the water you have the weight of the boat.

Last edited: Oct 23, 2007
3. Oct 23, 2007

### alister718

Buoyancy has nothing to do with it?

4. Oct 23, 2007

### Math Jeans

V_f would not allow you to know the weight of the boat, It would only allow you to know the volume of the boat. You must also know the material that the boat is made from in order to find the weight.

The displaced water dictates how much upward force is exerted on the boat.

5. Oct 23, 2007

### Staff: Mentor

That is buoyancy. That's what buoyancy is!
http://en.wikipedia.org/wiki/Buoyancy

6. Oct 23, 2007

### Staff: Mentor

No. Think about that a little more. Why would this tell you the volume of the boat? Most of the boat is not submerged! So the volume of water displaced is only the volume of the submerged portion of the boat....
Yes, and....? How much upward force does the floor exert on you...?

7. Oct 24, 2007

### alister718

if order to do this we would need to find the height of the boat that is not submerged

8. Oct 24, 2007

### Math Jeans

Sorry, I thougt that the implication was the the boat was fully submerged. My mistake.

9. Oct 24, 2007

### Staff: Mentor

No, no, no, no, no.

Look at the equation for buoyant force! You only need to know one thing (that isn't a constant) and you gave it in your opening post!

Last edited: Oct 24, 2007
10. Oct 24, 2007

### Staff: Mentor

A boat designed to run fully-submerged is called a "submarine"...

A boat that is not designed to run fully-submerged but is must have a hole (or holes) in it, so it's sunken displacement tells you nothing about its weight or volume.

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