Answer: A
Explanation: When a steel ball is thrown into a viscous liquid, three forces will act on the ball.
1.) The viscous drag force V which is acting upward
2.) The buoyant force U which is acting upward and
3.) The weight of the ball W. Which is acting downward.
When it is moving with an acceleration a, the weight W will be greater than U and V
Since Force = ma.
The resultant vector force will be
W - V - U = ma