**Question #1**

Consider fluid flow between two infinite horizontal plates which are parallel (the gap between them being 50 mm). The top plate is sliding parallel to the stationary bottom plate at a speed of 3 m/s.The flow between the plates is solely due to the motion of the top plate. The force per unit area (magnitude) required to maintain the bottom plate stationary is _________ N/m^{2}

Viscosity of the fluid µ = 0.44 kg/m-s and density = 888 kg/m^{3}

**[GATE 16 S2, 1 mark]**

**Question #2**

Which of the following statements are TRUE, when the cavitation parameter σ = 0?

(i) the local pressure is reduced to vapor pressure

(ii) cavitation starts

(iii) boiling of liquid starts

(iv) cavitation stops

(A) (i), (ii) and (iv)

(B) only (ii) and (iii)

(C) only (i) and (iii)

(D) (i), (ii) and (iii)

**[GATE 15 S3, 2 marks]**

**Question #3**

In a simple concentric shaft-bearing arrangement, the lubricant flows in the 2 mm gap between the shaft and the bearing. The flow may be assumed to be a plane Couette flow with zero pressure gradient. The diameter of the shaft is 100 mm and its tangential speed is 10 m/s. The dynamic viscosity of the lubricant is 0.1 kg/m.s. The frictional resisting force (in newton) per 100 mm length of the bearing is __

**[GATE14 S1, 2 marks]**

**Answer:15.7 N**

$F=\frac{\mu AV}{y}….(i)$

$A=\pi dL$

$A=\pi \times 0.1\times 0.1=0.0314m^2….(i)$

Therefore,

$F=\frac{0.1 \times 0.0314\times 10}{0.002}$

$F=15.7N…..(Answer)$

**Question #4**

Assuming constant temperature condition and air to be an ideal gas, the variation in atmospheric pressure with height calculated from fluid statics is

(A) linear

(B) exponential

(C) quadratic

(D) cubic

**[GATE 16 S2, 1 mark]**

**Question #5**

The difference in pressure (in N/m^{2}) across an air bubble of diameter 0.001 m immersed in water (surface tension = 0.072 N/m) is _______

**[GATE 14 S2, 1 mark]**

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