Concept:A ball moving through a viscous liquid is acted upon by its weight, upthrust, and viscous drag.
Explanation:The weight of the ball pulls it downward, given by
W=mg.
The liquid exerts an upthrust upward, which equals the weight of the liquid displaced by the ball.
As the ball falls, the viscous force of the liquid opposes the motion, so it acts upward.
These three forces act on the ball at the same time.
Therefore, the ball experiences the combined effect of upthrust, its weight, and viscous force.
Answer:D. upthrust, the ball's weight and viscous force