An air bubble in a tank of water is moving upwards at constant velocity. The forces acting on the bubble are $X$, $Y$ and $Z$ as shown. Which statement describes these three forces?
- A$Z$ is the viscous drag on the bubble, $Y$ is the weight of the bubble, $X$ is the upthrust on the bubble and $X = Y + Z$.
- B$Z$ is the viscous drag on the bubble, $Y$ is the weight of the bubble, $X$ is the upthrust on the bubble and $X > Y + Z$.
- C$Z$ is the weight of the bubble, $Y$ is the viscous drag on the bubble, $X$ is the upthrust on the bubble and $X = Y + Z$.
- D$Z$ is the weight of the bubble, $Y$ is the viscous drag on the bubble, $X$ is the upthrust on the bubble and $X > Y + Z$.