Hydrostatic Pressure MCQs – Part 2

Question 16Easy

An odd shaped body weighing 7.5 kg and occupying 0.01 cubic meter volume will be completely submerged in a fluid having specific gravity of ...............

Full explanation

Answer: D. 0.75

Body density = m / V = 7.5 / 0.01 = 750 kg/m³. For complete neutral submergence: S_fluid = ρ_body / ρ_water = 750 / 1000 = 0.75.

Question 17Medium

Estimate the distance to the centre of pressure below the free surface for a vertical triangular plane area submerged in water (as in the given figure) with one side on the free surface, vertex downward and altitude h.

Full explanation

Answer: D. h/2

Centroid h̄ = h/3. Centre of pressure h* = h̄ + I_G / (A h̄) = h/3 + (bh³/36) / [(bh/2)(h/3)] = h/3 + h/6 = h/2.

Question 18Medium

Determine the position of center of pressure (from the surface) for a rectangular lamina of height h vertically inside the water.

Full explanation

Answer: C. 2h/3

For a vertical rectangular lamina of height h with top edge at the water surface, the centre of pressure lies at h* = 2h/3.

Question 19Hard

Water is transported on a level road in the cylindrical container of diameter 0.5 m and height 0.8 m. The maximum acceleration of vehicle is 5 m/s². What is the initial allowable height of water (cm) in the tank, if there is no spill?

Full explanation

Answer: B. 67.3

Surface slope tan θ = a/g = 5/9.81 = 0.5097. Rise at lip = (d/2) tan θ = 0.25 × 0.5097 = 0.1274 m. Allowable depth = 0.80 − 0.1274 = 0.6726 m = 67.3 cm.

Question 20Easy

What is the depth of the center of pressure for the rectangular lamina which is vertically inside the water of height h ?

Full explanation

Answer: C. 2h/3

For a vertical rectangular lamina of height h starting from the water surface, the centre of pressure is at h* = 2h/3.

Question 21Hard

A longitudinal rectangular surface is hanged into the water such that its top and bottom points are at depth of 1.5 and 6.0 m respectively. The depth of center of pressure (m) from the top surface is ........

Full explanation

Answer: B. 4.2

Height h = 6.0 − 1.5 = 4.5 m; Centroid h̄ = 1.5 + 4.5/2 = 3.75 m. Centre of pressure h* = 3.75 + (4.5²/12)/3.75 = 3.75 + 0.45 = 4.20 m.

Question 22Medium

The pressure intensity is same in all directions at a point in a fluid :

Full explanation

Answer: B. Only when fluid is frictionless and is at rest

Pressure intensity is isotropic (Pascal's law) whenever shear stress is zero, which occurs when a fluid is at rest or has no relative motion between layers (Option b as per book key; Option d physically).

Question 23Easy

Centre of pressure on an inclined plane is .........

Full explanation

Answer: C. Below the centroid

Due to the positive term (I_G · sin²θ) / (A · h̄), the centre of pressure on an inclined plane always lies below the centroid.

Question 24Easy

Pascal's law states that pressure at any point in a fluid at rest has :

Full explanation

Answer: B. Same magnitude in all direction

According to Pascal's law, pressure at any point in a fluid at rest has the same magnitude in all directions.

Question 25Medium

A vessel containing water of depth h is accelerated upward with an acceleration of g/2. The pressure at the bottom of the vessel is?

Full explanation

Answer: D. 3γh/2

Effective gravity g_eff = g + a = g + g/2 = 3g/2. Pressure P = ρ · g_eff · h = 3/2 · ρgh = 3γh/2.

Question 26Easy

The point in the immersed body through which the resultant pressure of the liquid may be taken to act is known as ______ ?

Full explanation

Answer: C. centre of pressure

The point on an immersed surface through which the resultant hydrostatic force acts is known as the centre of pressure.

Question 27Medium

A rectangular plate 1.25 m × 2.4 m is immersed in a liquid of relative density 0.85 with its 1.25 m side horizontal and just at the water surface. If the plane of the plate makes an angle of 60° with the horizontal, the pressure force on one side of the plate is :

Full explanation

Answer: D. 26.0 kN

Centroid depth h̄ = (2.4/2)·sin 60° = 1.0392 m. Force P = ρ g A h̄ = (850 × 9.81) × (1.25 × 2.4) × 1.0392 = 25,996 N ≈ 26.0 kN.

Question 28Easy

The total pressure on the surface of a vertical sluice gate 2 m × 1 m with its top 2 m surface being 0.5 m below the water level will be ........

Full explanation

Answer: D. 2000 kg

Area A = 2 × 1 = 2 m²; Centroid h̄ = 0.5 + 1/2 = 1.0 m. Total pressure in kgf = ρ · A · h̄ = 1000 × 2 × 1.0 = 2000 kg.