Year 11 Science: Mechanics, Genetics & the Material World

Comprehensive review flashcards covering Level 1 Mechanics, Genetics & Variation, and Material World Chemistry.

How is average speed calculated over an entire journey?

Average speed is calculated as total distance divided by total time: $v_{\text{avg}} = \frac{d_{\text{total}}}{t_{\text{total}}}$, where distance is measured in metres ($\text{m}$) and time in seconds ($\text{s}$).

On a distance-time graph, what do the gradient and a flat horizontal line represent?

The gradient represents speed ($v$). A flat horizontal line indicates that the object is stationary ($v = 0\,\text{m}\,\text{s}^{-1}$).

On a speed-time graph, what do the gradient and the area beneath the line represent?

The gradient represents acceleration ($a = \frac{\Delta v}{\Delta t}$), and the total area beneath the line represents the distance travelled ($d = \text{area}$).

Using this speed-time graph, what is the combined distance travelled by the shuttle during Sections P and R while its speed was changing?

$480\,\text{m}$. Section P is a triangle: $\frac{1}{2} \times 40\,\text{s} \times 12\,\text{m}\,\text{s}^{-1} = 240\,\text{m}$. Section R is an identical triangle: $\frac{1}{2} \times 40\,\text{s} \times 12\,\text{m}\,\text{s}^{-1} = 240\,\text{m}$. Combined distance = $240\,\text{m} + 240\,\text{m} = 480\,\text{m}$.

What is the difference in motion between balanced ($F_{\text{net}} = 0\,\text{N}$) and unbalanced ($F_{\text{net}} \neq 0\,\text{N}$) forces?

When $F_{\text{net}} = 0\,\text{N}$ (Newton's First Law), forces are balanced and the object remains stationary or travels at constant velocity. When $F_{\text{net}} \neq 0\,\text{N}$ (Newton's Second Law), forces are unbalanced and the object accelerates in the direction of the net force ($F_{\text{net}} = ma$).

A cyclist and bicycle have a combined mass of $75\,\text{kg}$. If forward thrust is $180\,\text{N}$ and opposing resistive drag is $45\,\text{N}$, what is the initial acceleration?

$1.8\,\text{m}\,\text{s}^{-2}$ forwards. $F_{\text{net}} = F_{\text{thrust}} - F_{\text{drag}} = 180\,\text{N} - 45\,\text{N} = 135\,\text{N}$. Acceleration is $a = \frac{F_{\text{net}}}{m} = \frac{135\,\text{N}}{75\,\text{kg}} = 1.8\,\text{m}\,\text{s}^{-2}$.

What is the physical difference between mass and weight?

Mass ($m$) is the amount of matter in an object, measured in kilograms ($\text{kg}$), and remains constant everywhere. Weight ($F_g$ or $W$) is the downward gravitational force acting on that mass, measured in Newtons ($\text{N}$), calculated as $F_g = mg$ ($g = 10\,\text{N}\,\text{kg}^{-1}$ on Earth).

Why does Liam ($72\,\text{kg}$, boot area $0.056\,\text{m}^2$) sink into deep alpine snow while Aroha ($84\,\text{kg}$, snowshoe area $0.28\,\text{m}^2$) does not?

Sinking depends on pressure ($P = \frac{F}{A}$). Liam exerts $P = \frac{720\,\text{N}}{0.056\,\text{m}^2} \approx 12\,857\,\text{Pa}$, which exceeds the snow's supporting capacity. Aroha's snowshoes distribute her $840\,\text{N}$ weight over a much larger area, producing only $P = \frac{840\,\text{N}}{0.28\,\text{m}^2} = 3000\,\text{Pa}$.

Mere lifts a $24\,\text{kg}$ crate to a shelf $1.80\,\text{m}$ high in $2.0\,\text{s}$, while Tane lifts an identical $24\,\text{kg}$ crate to $1.20\,\text{m}$ in $1.0\,\text{s}$. Why is Tane's claim that Mere did more work but he was more powerful correct?

Mere did more work ($W = Fd = 240\,\text{N} \times 1.80\,\text{m} = 432\,\text{J}$ vs Tane's $288\,\text{J}$) because she lifted through a greater height. Tane had higher power output ($P = \frac{W}{t} = \frac{288\,\text{J}}{1.0\,\text{s}} = 288\,\text{W}$ vs Mere's $216\,\text{W}$) because power is the rate of doing work.

In an ideal, frictionless system, how is the speed of an object at the bottom of a ramp related to its starting vertical height?

All gravitational potential energy transforms into kinetic energy: $\Delta E_p = E_k \implies mgh = \frac{1}{2}mv^2$. Solving for speed gives $v = \sqrt{2gh}$.

What are the three structural components of a single DNA nucleotide?

A phosphate group, a deoxyribose sugar, and one of four nitrogenous bases: Adenine ($\text{A}$), Thymine ($\text{T}$), Cytosine ($\text{C}$), or Guanine ($\text{G}$).

How does a gene differ from an allele?

A gene is a specific sequence of DNA bases that codes for a functional protein. An allele is an alternative version of that gene with a slightly different base sequence, coding for an altered protein and physical trait.

How do somatic mutations differ from gametic mutations in their inheritance and evolutionary impact?

Somatic mutations occur in body cells during mitosis, cannot be passed to offspring, and do not enter the gene pool. Gametic mutations occur in cells producing gametes during meiosis and can be inherited via fertilisation, introducing new alleles to the population gene pool.

Which two processes during meiosis generate unique combinations of alleles in gametes?

Crossing over (the exchange of chromosome segments between non-sister chromatids of homologous chromosomes) and independent assortment (the random alignment and separation of maternal and paternal chromosomes).

In this pedigree chart, what evidence proves that the condition is inherited as an autosomal recessive allele?

Unaffected parents (I-1 and I-2) produce an affected child (II-2). If the allele were dominant, at least one parent would also show the phenotype. Therefore, both parents must be heterozygous carriers ($Nn$) who passed their recessive allele ($n$) to an affected child ($nn$).

What is the difference between discrete variation and continuous variation?

Discrete variation consists of distinct, separate categories controlled by a single gene and is unaffected by the environment (e.g. human ABO blood types). Continuous variation shows a complete numerical gradient controlled by multiple genes interacting with environmental influences (e.g. height, kiwi body mass).

Why are atomic numbers always whole integers while relative atomic masses on the periodic table are decimals?

Atomic numbers count protons, which are indivisible whole particles. Relative atomic mass is a weighted average of all naturally occurring isotopes of an element, taking into account their differing mass numbers and natural abundances.

Why do a sulfide ion ($S^{2-}$) and a calcium ion ($Ca^{2+}$) have the same electron configuration ($2,8,8$) but opposite charges?

Sulfur ($2,8,6$) gains 2 electrons to complete its valence shell, giving 18 electrons and 16 protons ($S^{2-}$). Calcium ($2,8,8,2$) loses 2 valence electrons, giving 18 electrons and 20 protons ($Ca^{2+}$). They are isoelectronic but oppositely charged due to proton-electron imbalances.

Why does a $Ca^{2+}$ ion have a smaller ionic radius than an isoelectronic $S^{2-}$ ion?

Both ions share the identical $2,8,8$ electron arrangement and shielding, but $Ca^{2+}$ has 20 protons compared to $S^{2-}$'s 16 protons. The greater positive nuclear charge in $Ca^{2+}$ exerts a stronger electrostatic pull, drawing the electron shells closer to the nucleus.

According to collision theory, what two criteria are required for a collision between reactant particles to result in a chemical reaction?

Reactant particles must collide with the correct collision orientation and possess kinetic energy equal to or greater than the activation energy ($E \ge E_a$).

Why does increasing temperature cause a substantial increase in the rate of a chemical reaction?

Particles gain kinetic energy and move faster, increasing collision frequency. More importantly, a much higher proportion of particles possess energy equal to or exceeding the activation energy ($E \ge E_a$), dramatically increasing the frequency of successful collisions per unit time.

In the disappearing cross reaction between sodium thiosulfate and hydrochloric acid, what causes the cross to become obscured?

The formation of a cloudy, insoluble fine yellow-white precipitate of solid sulfur: $Na_2S_2O_3(aq) + 2HCl(aq) \rightarrow 2NaCl(aq) + SO_2(g) + S(s) + H_2O(l)$.

How can unlabelled samples of $MgCl_2$, $MgO$, and $MgCO_3$ be distinguished using deionised water, universal indicator, and dilute $HCl$?

$MgCl_2$ dissolves in water forming a neutral solution (indicator turns green). $MgO$ and $MgCO_3$ are insoluble ($MgO$ is basic, turning indicator blue/purple). When dilute $HCl$ is added, $MgCO_3$ fizzes vigorously releasing $CO_2$ gas, whereas $MgO$ dissolves cleanly without fizzing.

What is the net ionic equation for the reaction between solid magnesium carbonate and hydrochloric acid?

$MgCO_3(s) + 2H^+(aq) \rightarrow Mg^{2+}(aq) + CO_2(g) + H_2O(l)$. Chloride ions ($Cl^-(aq)$) are spectator ions and cancel out.

Based on the reactivity series, what is observed when magnesium ribbon is placed into copper(II) sulfate ($CuSO_4$) solution, and why?

A reddish-brown solid of copper forms because magnesium is more reactive than copper and displaces $Cu^{2+}$ ions from solution: $Mg(s) + CuSO_4(aq) \rightarrow MgSO_4(aq) + Cu(s)$.

What structural feature of ionic compounds accounts for their high melting points?

Ionic compounds form a continuous giant 3D lattice held together by strong electrostatic attractions acting in all directions between oppositely charged cations and anions, requiring substantial thermal energy to break.

Why does magnesium oxide ($MgO$, m.p. $2852\,^\circ\text{C}$) have a much higher melting point than sodium chloride ($NaCl$, m.p. $801\,^\circ\text{C}$)?

Both form 3D ionic lattices, but $MgO$ contains doubly charged ions ($Mg^{2+}$ and $O^{2-}$), whereas $NaCl$ contains singly charged ions ($Na^+$ and $Cl^-$). The electrostatic attraction between $+2$ and $-2$ charges is much stronger, requiring significantly more heat energy to break the bonds.