4.2. Force Analysis

Try these first

1. 1.

   Define mass conservation in your own words.

   Hint

   Consider what happens to mass in closed versus open systems.

2. 2.

   What is incompressible flow?

   Hint

   Think about how water behaves under normal conditions.

3. 3.

   What does the mass conservation principle state?

   • Mass can be created
   • Mass remains constant in a closed system
   • Mass leaves the system

   Hint

   Consider your understanding of closed versus open systems.

4. 4.

   Is incompressible flow characterized by constant density?

   • True
   • False

   Hint

   Relate it to how water behaves under pressure.

5. 5.

   Given a flat plate is moving at 10 m/s into a water jet with a velocity of 25 m/s, if the water density is 1000 kg/m^3 and the jet area is 0.05 m^2, calculate the net force exerted on the plate considering the jet splits equally.

   Hint

   Use momentum equations involving relative velocities.

6. 6.

   A spacecraft with a mass of 10000 kg is dropping towards Earth at a speed of 600 m/s. If it expels gas with a rate of 50 kg/s at a speed of 2000 m/s, calculate the thrust produced and how much force counteracts gravity (approximation 98000 N).

   Hint

   Incorporate mass flow rate with exhaust velocity in your calculations.