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Name metals that resist corrosion.
Gold and platinum are very unreactive and do not corrode readily. Silver also resists ordinary oxidation, although sulphur compounds can tarnish it.
Gold and platinum.
Under what soil condition should a farmer add quicklime, slaked lime or chalk? Explain the treatment.
Quicklime, slaked lime and chalk are basic substances. They are added when soil is too acidic, that is, when its pH is below the range suitable for the crop. The base neutralises excess soil acid and raises the pH towards the optimum value. The amount should be selected after testing the soil because excessive lime can make the soil too alkaline.
They are used for acidic soil to neutralise excess acid and raise its pH.
Room-temperature molar Cv values for
Principle and reasoning. Work from the governing physical relation and apply it to every stated part.
Equipartition assigns (\(\frac{1}{2}\))R per mole to each active quadratic degree of freedom. A monatomic ideal gas has three translational degrees, so Cv=3R/2≈2.98 cal mol⁻¹ K⁻¹. A diatomic molecule also has two active rotational degrees at room temperature, giving Cv=5R/2≈4.97 cal mol⁻¹ K⁻¹.
Chlorine's larger value signals that vibrational motion is already partly excited at room temperature. Vibrational modes add kinetic and potential energy contributions, raising Cv above 5R/2.
A horizontal pipe narrows at a throat. Sketch A shows a higher piezometer column at the throat; sketch B shows a lower column there. Which sketch is inconsistent with steady inviscid flow?
Principle. Continuity makes the throat speed larger. At equal height, Bernoulli's equation therefore requires lower static pressure at the throat, which must produce a lower piezometer level.
A solid copper cube of side \(10.0\,\mathrm{cm}\) is exposed to a uniform pressure increase of 7.0×10⁶ Pa. Find its volume contraction using Bcopper=1.4×10¹¹ Pa.
Principle. The volume change follows |ΔV|=VΔP/B.
Volume contraction = 5.0 × 10⁻⁸ m³ (0.050 cm³).
A uniform disk of radius R has a circular hole of radius \(\frac{R}{2}\) cut with its centre \(\frac{R}{2}\) from the disk centre. Locate the remaining lamina's centre of mass.
Principle. Represent the hole as negative mass. Mass is proportional to area, so the removed disk has one quarter of the original mass.
Blocks of \(10\,\mathrm{kg}\) and \(20\,\mathrm{kg}\) are tied on a smooth table. A 600 N horizontal pull is applied first to the \(20\,\mathrm{kg}\) block and then to the \(10\,\mathrm{kg}\) block. Find string tension in each arrangement.
Principle. Both blocks share acceleration F divided by total mass. Tension is the force accelerating the block not directly pulled.
An aircraft flies a level circle of radius \(1.00\,\mathrm{km}\) at \(900\,\mathrm{km\,h^{-1}}\). Express its centripetal acceleration as a multiple of g.
Principle. Uniform circular acceleration is v squared divided by radius.
For three qualitative motion graphs, give a plausible real event matching each: a stepped position history, a bouncing position history, and a sharp velocity reversal.
Principle. Translate horizontal portions as rest, straight slopes as uniform velocity, curved free-flight arcs as acceleration and a near-vertical velocity change as an impulse.
At STP one mole of ideal gas fills 22.4 L. Estimate
Principle. Compare the molar gas volume with Avogadro's number times the volume of one molecular-sized sphere.