Online Test — Mechanical Properties of Fluids
18 Questions • 15 min • Chapter MCQ
15:00
Question 1 of 18
The SI unit of pressure is:
newton
pascal
joule
watt
Explanation: Pressure $P=\frac{F}{A}$ has unit $\text{N/m}^2=$ pascal.
Question 2 of 18
The pressure at depth $h$ in a liquid open to the atmosphere is:
$\rho gh$
$P_0-\rho gh$
$P_0+\rho gh$
$P_0\rho gh$
Explanation: $P=P_0+\rho gh$, surface pressure plus the column pressure.
Question 3 of 18
Pascal's law is used in a:
barometer
hydraulic brake
thermometer
voltmeter
Explanation: Hydraulic brakes transmit pressure undiminished through an enclosed fluid.
Question 4 of 18
In a hydraulic lift with $A_2>A_1$, the output force $F_2$ equals:
$F_1\frac{A_1}{A_2}$
$F_1\frac{A_2}{A_1}$
$F_1 A_1 A_2$
$\frac{F_1}{A_1 A_2}$
Explanation: Equal pressure gives $F_2=F_1\frac{A_2}{A_1}$.
Question 5 of 18
Atmospheric pressure at sea level is about:
$1.013\times10^3\ \text{Pa}$
$1.013\times10^5\ \text{Pa}$
$76\ \text{Pa}$
$9.8\ \text{Pa}$
Explanation: 1 atm $\approx1.013\times10^5\ \text{Pa}$, supporting 76 cm of mercury.
Question 6 of 18
The buoyant force on a submerged body equals the:
weight of the body
weight of fluid displaced
volume of the body
pressure at the surface
Explanation: Archimedes' principle: $F_B=V_{disp}\rho g$.
Question 7 of 18
An object floats when its average density is:
greater than the fluid's
less than the fluid's
equal to $g$
infinite
Explanation: A body floats if its density is less than that of the fluid (law of flotation).
Question 8 of 18
The viscous drag on a small sphere is given by Stokes' law as:
$6\pi\eta r v$
$\frac{6\pi r v}{\eta}$
$6\pi\eta r^2 v$
$\pi\eta r v^2$
Explanation: Stokes' law: $F=6\pi\eta r v$.
Question 9 of 18
The terminal velocity of a sphere in a viscous fluid varies as:
$r$
$r^2$
$\frac{1}{r}$
$r^3$
Explanation: $v_t=\frac{2r^2(\rho-\sigma)g}{9\eta}\propto r^2$.
Question 10 of 18
The equation of continuity is:
$A_1v_1=A_2v_2$
$P_1=P_2$
$\frac{v_1}{A_1}=\frac{v_2}{A_2}$
$A_1v_2=A_2v_1$
Explanation: Volume flow rate is constant: $A_1v_1=A_2v_2$.
Question 11 of 18
Where a pipe narrows, the speed of an incompressible fluid:
decreases
increases
stays the same
becomes zero
Explanation: From $Av=\text{const}$, smaller $A$ means larger $v$.
Question 12 of 18
Bernoulli's equation states that the quantity that is constant along a streamline is:
$P+\rho gh$
$\frac{1}{2}\rho v^2$
$P+\frac{1}{2}\rho v^2+\rho gh$
$P v$
Explanation: $P+\frac{1}{2}\rho v^2+\rho gh=\text{constant}$ along a streamline.
Question 13 of 18
According to Bernoulli, regions of high fluid speed have:
high pressure
low pressure
zero pressure
infinite pressure
Explanation: Higher $v$ means a smaller $P$ so the sum stays constant.
Question 14 of 18
Surface tension has the SI unit:
$\text{N}$
$\text{N/m}$
$\text{N}\cdot\text{m}$
$\text{Pa}$
Explanation: $T=\frac{F}{L}$ is force per unit length, in N/m.
Question 15 of 18
The capillary rise of a liquid is given by:
$h=\frac{2T\cos\theta}{\rho g r}$
$h=\frac{\rho g r}{2T}$
$h=2T\rho g r$
$h=\frac{T r}{\rho g}$
Explanation: $h=\frac{2T\cos\theta}{\rho g r}$, greater for narrower tubes.
Question 16 of 18
The excess pressure inside a liquid drop of radius $R$ is:
$\frac{T}{R}$
$\frac{2T}{R}$
$\frac{4T}{R}$
$\frac{T}{2R}$
Explanation: A drop has one surface, so $P_{excess}=\frac{2T}{R}$.
Question 17 of 18
The excess pressure inside a soap bubble compared with a liquid drop of the same radius is:
the same
half
double
four times
Explanation: A soap bubble has two surfaces ($\frac{4T}{R}$), twice the drop's $\frac{2T}{R}$.
Question 18 of 18
The angle of contact of water with clean glass is:
obtuse
acute
$90^\circ$
$180^\circ$
Explanation: Water wets glass, giving an acute angle of contact and a concave meniscus.