Properties of Bulk Matter Questions and Answers

Answer: B

The change in kinetic energy per kg is \(2 \times 10^{-3}\) J kg^-1.

For a horizontal pipe, Bernoulli's equation gives \(\Delta p = \Delta\left(\tfrac{1}{2}\rho v^{2}\right)\). Dividing by the density gives the change in kinetic energy per unit mass.

\[ \begin{aligned} \frac{\Delta p}{\rho} &= \frac{1.6}{800} \\ &= 2 \times 10^{-3}\ \text{J kg}^{-1} \end{aligned} \]

The 1 m separation does not enter the calculation. \(16 \times 10^{-4}\) and \(8 \times 10^{-4}\) come from misplacing the decimal or halving.

Answer: B

The surface tension is \(\frac{W}{4A}\).

A soap film has two surfaces, so increasing its area from A to 3A creates \(2 \times 2A = 4A\) of new surface.

\[ W = T \times 4A \Rightarrow T = \frac{W}{4A} \]

\(\frac{W}{2A}\) would ignore the two surfaces (it is not offered), and \(\frac{W}{A}\) or \(\frac{W}{3A}\) use the wrong change in area. WA and 2WA have the wrong dimensions. Surface tension is the work done per unit area of new surface, measured in J m^-2 or N m^-1.

Answer: E

The mismatch is Vapour to solid : regelation.

The direct change from vapour to solid is called deposition (or desublimation). Regelation is the melting of ice under pressure and its refreezing when the pressure is removed, as when a loaded wire passes through a block of ice.

The other pairs are correct: solid to liquid is melting, liquid to solid freezing, liquid to vapour vaporisation, and solid to vapour sublimation.

Answer: D

The hydraulic brake is a direct application of Pascal's Law.

Pascal's law states that pressure applied to an enclosed fluid is transmitted undiminished to every part of the fluid and the walls of its container. In a hydraulic brake, pressing the pedal pushes a small piston in the master cylinder; the pressure passes through the brake fluid to the wheel cylinders, whose larger pistons push the brake shoes or pads. Because force equals pressure times area, a small force at the pedal becomes a large braking force at the wheels.

Archimedes' principle concerns buoyancy, Torricelli's law the speed of liquid flowing out of an opening, and Bernoulli's theorem the link between speed and pressure in a moving fluid. None explains pressure transmission in a closed brake line.