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?