Bennett Mechanical Fluid Mechanics and Hydraulics Questions and Answers 1 — Questions and Answers
Question 1: A hydraulic press has a small piston with an area of 2 square inches and a large piston with an area of 20 square inches. If a force of 50 lbs is applied to the small piston, what is the maximum weight the large piston can lift?
- 5 lbs
- 50 lbs
- 500 lbs (Correct answer)
- 1000 lbs
Correct answer: 500 lbs
According to Pascal's principle, pressure applied to an enclosed fluid is transmitted equally throughout. Pressure is Force divided by Area (P = F/A). Therefore, the pressure on the small piston (P1) is equal to the pressure on the large piston (P2), so F1/A1 = F2/A2. The force is multiplied by the ratio of the areas (20 in² / 2 in² = 10). The output force is 10 times the input force: 50 lbs * 10 = 500 lbs.
Question 2: Water flows steadily through a pipe that narrows from point X to point Y. Which of the following statements is true about the water's velocity?
- The velocity is greater at point X than at point Y.
- The velocity is the same at both points.
- The velocity is greater at point Y than at point X. (Correct answer)
- The velocity decreases to zero at point Y.
Correct answer: The velocity is greater at point Y than at point X.
Based on the principle of continuity for an incompressible fluid, the mass flow rate must remain constant. This means the product of the cross-sectional area and the fluid velocity is constant (A1*V1 = A2*V2). Since the area at point Y is smaller than the area at point X, the velocity of the water must be greater at point Y to maintain the same volume of water flowing per unit of time.
Question 3: Three solid, sealed objects of identical size and shape are fully submerged in a tank of water. Object A is made of wood, Object B is made of aluminum, and Object C is made of lead. Which object experiences the greatest buoyant force?
- Object A
- Object B
- Object C
- They all experience the same buoyant force. (Correct answer)
Correct answer: They all experience the same buoyant force.
Archimedes' principle states that the buoyant force on a submerged object is equal to the weight of the fluid displaced by the object. Since all three objects have the identical size and shape, they displace the same volume of water. Therefore, the weight of the displaced water is the same for all three, and they each experience an identical buoyant force, regardless of their own weight or density.
Question 4: The diagram shows a dam holding back a large body of water. At which point is the hydrostatic pressure against the face of the dam the greatest?
- Point A (near the surface)
- Point B (halfway down)
- Point C (near the bottom) (Correct answer)
- The pressure is uniform at all depths.
Correct answer: Point C (near the bottom)
Hydrostatic pressure increases linearly with depth. The formula for fluid pressure is P = ρgh, where ρ is the fluid density, g is the acceleration due to gravity, and h is the depth below the surface. Therefore, the pressure is lowest at the surface (Point A) and greatest at the deepest point (Point C). This is why dams are constructed to be much thicker at the base.
Question 5: Two ships are sailing at high speed, parallel to each other and in close proximity. Due to Bernoulli's principle, what is the most likely interaction between the ships?
- They will be pushed apart.
- They will be pulled toward each other. (Correct answer)
- Their speed will increase.
- There will be no noticeable effect.
Correct answer: They will be pulled toward each other.
According to Bernoulli's principle, an increase in the speed of a fluid occurs simultaneously with a decrease in pressure. The water flowing in the narrow channel between the two ships moves faster than the water on their outer sides. This creates a region of lower pressure between them. The higher pressure on the outer sides of the ships then pushes them toward each other.
Question 6: For a siphon to successfully transfer water from a higher container to a lower container, which of the following conditions is essential?
- The outlet of the siphon tube must be below the water level of the source container. (Correct answer)
- The highest point of the tube must be below the water level of the source container.
- Both containers must be at the same atmospheric pressure.
- The diameter of the tube's outlet must be larger than its inlet.
Correct answer: The outlet of the siphon tube must be below the water level of the source container.
A siphon works because the weight of the water in the longer, downward leg of the tube creates a pressure difference that pulls water up the shorter leg. For this to happen, the final outlet of the tube must be at a lower elevation than the surface of the liquid in the source container. This height difference provides the gravitational potential energy needed to drive the flow.
Bennett Mechanical Fluid Mechanics and Hydraulics Questions and Answers 1
A hydraulic press has a small piston with an area of 2 square inches and a large piston with an area of 20 square inches.
If a force of 50 lbs is applied to the small piston, what is the maximum weight the large piston can lift?