# 2 spheres in an ocean

1. May 17, 2007

### aff67611

1. The problem statement, all variables and given/known data
Two spheres, with volume 0.1m^3, and masses M1=200kg and M2=15kg, are connected by a thin wire. They are dropped into the ocean (assume Rho=1000kg/m^3) and allowed to sink

2. Relevant equations

3. The attempt at a solution
I know buoyancy = Rho * g * V
Buoyancy + Lift-M2 + Fwire = Sink-M1.

I'm not sure how to get the rising/sinking forces of the two spheres, and how they interact with each other though.

Any help at all is appreciated, thanks in advance.

2. May 17, 2007

### Hootenanny

Staff Emeritus
Welcome to the forums,

Well initially, I think it would be best if we considered each sphere independently. So, can you write two separate equations for the net force acting on each sphere?

3. May 17, 2007

### aff67611

My best guess would be:

Heavy (case1). mg = downwards force - buoyancy. DownwardsF = 200g - 981N = 981N?

I'm not sure how the lighter sphere will act though. If it's specific density is lower than 1 then only part of the sphere will be submerged if it's acting seperately?

4. May 17, 2007

### Hootenanny

Staff Emeritus
For the heavy one, I was thinking something more of the form (taking upwards as positive);

$$F_{net} = T + \rho\cdot V\cdot g - m_{1}g$$

Where T is the tension in the string. Does that make sense?