# Calculate mass of tank floating in freshwater

1. May 28, 2016

### Parsifal1

1. The problem statement, all variables and given/known data
A rectangular tank contains 6L of freshwater, has a floor area of 0.3m^2 and floats upright in freshwater. If the bottom of the tank is 150mm below the surface of the water, calculate the mass of the tank.

2. Relevant equations
F=P*A=pgAh

3. The attempt at a solution
1000*9.81*0.3*0.15=441.54N 441.45/9.81=45kg

2. May 28, 2016

### billy_joule

I think you're expected to find the mass of just the tank( excluding the water).

3. May 28, 2016

### Parsifal1

That's what I don't understand, 6L=6Kg, should it be mass=0.03*1000=mass*density?

4. May 28, 2016

### billy_joule

You've found the mass of the tank and water in post #1; 45kg.
If there's 6kg of water in the tank, how much does just the tank weigh?

5. May 29, 2016

### Parsifal1

-15Kg? How can the mass of the tank and the water weigh less than the water? Am I using the right formula for the mass of the tank+water?

6. May 29, 2016

### Parsifal1

Should I do 0.3*0.15*1000=P=pyh=45 Then take 45 from 60? I get the wrong answer by doing that? :/

7. May 29, 2016

### Parsifal1

If the weight of the water displace=buoyant force, then is the mass of the tank the buoyant force over 9.81? As the mass of the object is equal to the mass of water displaced.

8. May 29, 2016