If they expect you to neglect hydrodynamic friction (drag), use
a = F/m to get the acceleration a,
where F is the weight minus the buoyancy force.
The accleration is up in both cases.
In the real world, drag will be important in reducing a and will depend upon the diameter and the velocity. Drag can be neglected the instant the ball is released, becasue it is not moving yet.
Two balls of the same volume are released inside a tank filled with water as shown in the figure. The densities of balls A and B are 0.86 g/cm3 and 0.55 g/cm3. (The density of water is 1.00 g/cm3. Take the +y direction to be up. Indicate the direction with the sign of your answer.)
(a) Find the acceleration of ball A.
(b) Find the acceleration of ball B.
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