State the conditions needed for a system to be in equilibrium.
Fig. 3.1 illustrates an airship in flight. It is driven by identical fans that may be tilted to adjust the airship's motion. The upthrust acting on the airship is $93000\,\text{N}$. The density of the surrounding air is $1.2\,\text{kg m}^{-3}$.
Calculate the volume of air displaced by the airship.
When fully loaded, the airship's weight exceeds the upthrust. To keep moving horizontally, the fans supply a total upward force of $3.0 \times 10^3\,\text{N}$ on the airship. Calculate the mass of the airship.
At a particular moment, the airship in (b) is at rest. The thrust force produced by a fan on the airship is $2800\,\text{N}$. To generate this force, a mass of $64\,\text{kg}$ of air is pushed through the fan blades in $0.50\,\text{s}$. Assume that this air is initially at rest at the fan entry. Calculate:
the change in momentum $\Delta p$ of the air pushed through the fan blades in this time.
the speed of the air as it leaves the fan.
the total kinetic energy of this air due to its motion through the fan.