Bennett Mechanical Fluid Mechanics and Hydraulics 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?

Accepted Answer

500 lbs

Answer

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?

Accepted Answer

The velocity is greater at point Y than at point X.

Answer

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?

Accepted Answer

They all experience the same buoyant force.

Answer

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?

Accepted Answer

Point C (near the bottom)

Answer

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?

Accepted Answer

They will be pulled toward each other.

Answer

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.

Bennett Mechanical Test Practice Test

Bennett Mechanical Test Practice Test

Bennett Mechanical Fluid Mechanics and Hydraulics Questions and Answers