A paint-spraying device is made of a box whose axes are horizontal and vertical. Small holes are cut in one of its vertical sides. Paint is supplied to the box under pressure through a vertical tube and then leaves through the holes as thin jets travelling horizontally. The paint leaves at a speed of $2.5\,\text{m s}^{-1}$ through $400$ holes, each with an area of $0.4\,\text{mm}^2$. The density of the paint is $900\,\text{kg m}^{-3}$. Determine the horizontal force needed to keep the device at rest while the paint is being ejected.
- A$0.36\,\text{N}$
- B$0.90\,\text{N}$
- C$2.3\,\text{N}$
- D$900\,\text{N}$